Proceedings of the 18th Conference of the Associated Research Centers for the Urban Underground Space

Underground architecture is frequently associated with urban densification and lack of buildable land. With Japan being home to some of the densest metropolises while lacking in constructible terrain, this conception has been solidified in recent years making it rare to find research observing underground space in a different and more nuanced manner. This paper aims to establish a comprehensive understanding of the contemporary role of Japanese underground architecture by consulting all projects in “Shinkenchiku” magazine between 2000 and 2020, identifying underground projects, collecting structured information, and examining its uses and adaptability. The data showed no increase in underground projects during the study period, contradicting past speculations. Although the results showed that underground projects are still being realized in dense urban areas, an approximately equal number is also found being constructed in rural areas with no constraints of available terrain. The findings challenge the prevailing notion that underground architecture primarily addresses space scarcity and densification issues, putting those assumptions under questioning, and suggesting the need for further research.

The work environment plays an important role in shaping the job satisfaction and retention of workers. Previous studies have suggested a link between underground work and worker satisfaction, with underground workers being less satisfied with their workplace. This study examines the relationship between worker satisfaction with work Indoor Environment Quality (IEQ), job satisfaction, and turnover intent in underground and aboveground workplaces. A questionnaire was administered to 401 workers in underground and aboveground workplaces in Singapore. The questionnaire focused on three main factors: IEQ satisfaction, job satisfaction, and turnover intent. Structural equation modelling was used to investigate the relationship between these factors, specifically, whether IEQ satisfaction predicted job satisfaction and turnover intent, and whether there were any differences between underground and aboveground workplaces or worker roles. The results indicated that worker satisfaction with IEQ had a significant positive effect on job satisfaction and a significant negative effect on turnover intent. While there was no significant effect of work location (above or underground), subgroup analyses showed that underground workers showed a stronger link between IEQ satisfaction and job satisfaction. In addition, differences were found between worker roles. Office and control room workers showed significant effects of IEQ satisfaction on job satisfaction and turnover intent. In comparison, workshop workers did not show significant effects. This study highlights the importance of worker satisfaction with their environment in shaping job satisfaction and the willingness to leave a job. The results suggest that companies with underground workspaces should prioritize creating a comfortable indoor environment to improve worker job satisfaction and reduce turnover. The findings also suggest that the effect of the work environment on worker attitudes and intentions is influenced by the worker role. Overall, the findings have important implications for underground workplace policies and practices aimed at improving worker retention and job satisfaction.

The urban ecosystem provides services that help humans lead physically and mentally healthy lives. However, pressure on urban areas increases due to demographic and climate change. Thus, urban underground space (UUS) offers a possible solution to achieve healthy, adaptive, and livable urban areas. Society has long made use of underground systems to enhance human health (e.g., through sewage and wastewater removal), deliver vital services (e.g., water, utilities), provide climate or security isolation and containment, reduce construction and energy costs, improve transportation and traffic flow, and achieve various aesthetic benefits. Based on the classification of Urban Underground Ecosystem Services (UUES) and their possible interactions with urban above and underground spaces, this study proposes four scenarios to explore how underground spaces can maintain the stability and sustainability of urban ecosystem services. The results show that the underground can continue to provide long-term, space-specific, or region-specific ecosystem services critical to maintaining and improving human well-being. This would help fully recognize the role underground space use plays in ecosystem services.

This paper examines the potential of underground spaces adjacent to metro stations as vibrant spaces of urban development. It discusses the possibilities of going beyond their mere transport-related function as communication hubs into spaces that prosper the community. The paper highlights the economic and social benefits of using underground spaces for retail, leisure, and public activities, showcasing examples of underground city centers.

Stable internal air temperatures are a defining characteristic of high thermal mass buildings, a tenet consistent with subterranean and earth-sheltered buildings. This paper introduces independent, evidence-based research from two earth-sheltered projects (18 buildings) providing empirical data in support of the premise that, ‘high thermal mass buildings should be the building form of choice in reducing heating/cooling loads together with concomitant greenhouse gas emissions’. The phenomenon responsible for stabilizing internal air temperatures in high thermal mass buildings is referred to by this author as a ‘residual heat reservoir’. This is the presence of a body of heat energy retained within the superstructure, sufficient to sustain habitable internal air temperatures, with low to no heating loads. In the first of two earth-sheltered projects, ‘Hoddins Way’ (Lincolnshire, 2009) [1] nine offices, the residual heat reservoir was identified, measured, and quantified. The recorded average internal air temperature was 22.2 C, experiencing an annual temperature variance of eight degrees centigrade (±4 °C) with an exceptionally low supplementary heating load of 9.1 KWh/m2/year. The second project is ‘Howgate Close’ (Nottinghamshire, 2022) [2] nine dwellings, same design principles with an improved construction specification, to optimize the reservoir of heat. After 10 months of occupation, average internal air temperature is circa 22 C (±2 °C) achieved with no heating load. Viewing high thermal mass buildings as reservoirs of heat energy with an active thermal core, assists in understanding how to usefully employ heavy building materials, allied with super-insulated and passive solar techniques for a more environmentally responsible form of development.

The design of metro stations, together with the artistic, cultural and media devices that populate underground metropolitan transport networks, is a field of study still predominantly in the realm of technology. Up to date, its increasingly important connection with the Historic Urban Landscape Approach championed by UNESCO remains understudied, particularly from a critical perspective. This paper aims to address this challenge by placing the cultural heritage discourse at the centre of the analysis of metro networks, from their planning, construction and subsequent use, understanding their extraordinary impact on the ways in which cities are lived and represented. The paper introduces four cases in Spain and one case in China: Seville, Malaga, Granada and Shanghai, with recent metro infrastructures and a high profile as heritage cities. Through visual methods, discourse analysis, interviews and direct observation, this paper presents the HUL_UG project developed by the author at the University of Seville. The project addresses underground metropolitan transport networks as heritage systems of enormous complexity, ranging from their controversial relationship with archaeology to their impact on city branding, including the role of metro station design in the historic urban landscape; its impact on tourism, and its link with social processes such as gentrification.

Cultural landscapes are one of the most important parts of the metropolises of the world. These spaces can be available to citizens as public spaces and increase cultural and social interactions. The spatial quality of these places can affect the quality of urban space and the lifestyle of citizens. Tehran Laleh Park complex, which is located in the center of Tehran city with an area of more than 35 hectares, is considered one of the cultural sights of Tehran city. Two museums of Contemporary Arts and Carpets were built in the west and northwest of this park in 1977 and 1978, respectively. Both of these buildings are considered to be the richest and most important museums in Iran; and also, they are two of the distinguished buildings in terms of architecture. In the open area around the Museum of Contemporary Art, there are valuable sculptures of the most famous artists in the world, which are currently not understood due to the visual disturbance caused by the existence of a disproportionate function. The open space between these two museums was supposed to be used for holding ceremonies and artistic events, but after the revolution and in 1988, a market was built under the name of Passage of Culture and Art, which then became a self-employed bazaar. This bazaar, which was supposed to be a place for the exchange of artworks, has now become a place for handicrafts and retail. It was built with a different concept and uncoordinated architecture between these two cultural buildings, which caused a visual disturbance and spatial disharmony in this part of the city. It seems that by using underground architecture, it is possible to coordinate with the park complex and its site by applying spatial changes, reducing density on the ground, developing the landscape, and transferring functions different from cultural purposes to the lower ground levels (In order to consider technical and executive matters). This article aims to examine this issue and how to increase open urban spaces and eliminate visual inconsistencies from the cultural perspective of Tehran Laleh Park.

Urban areas often contain interconnected underground resources, such as underground space, groundwater, shallow geothermal energy, and geological materials. Current evaluations of geological resources tend to focus on individual resources, neglecting a comprehensive assessment from a holistic perspective. This limitation has led to conflicts in resource development, compromised resource potential, and missed opportunities for synergistic resource utilization. In this study, the geologic body of Danyang City, where a comprehensive geologic survey has been conducted at a depth of 30m below the surface, is taken as the research object. Based on the division of regional geological units, the study assesses the endowment level of individual resources and proposes a “zonation radar chart” method to depict the comprehensive resource endowment of geological formations. Additionally, the study explores the application of this method in urban development planning, highlighting its significance in facilitating sustainable resource management and maximizing resource development opportunities.

Rational utilization and development of underground space, orderly arrangement of multiple functions in underground space, and forming underground complex system, is one of the effective ways to alleviate the contradiction of land resource shortage, and also one of the ways of sustainable development of green buildings. In the underground space complex project, the drainage problem is undoubtedly a very important aspect. Under geological conditions of collapsible loess, rainwater infiltration can easily lead to structural damage of collapsible loess and cause significant deformation of underground complex project. Therefore, how to collect and recycle the infiltration rainwater efficiently and safely is not only crucial for alleviating urban waterlogging, weakening surface water pollution, and stabilizing underground complex project, but also in line with the sustainable development concept of sponge city. Based on the Xi'an Happiness Forest Belt construction project, the rainwater treatment system has been optimized from design to construction. It can not only improve the rainwater treatment efficiency, but also better control the structure deformations caused by the collapsible loess damage caused by the rainwater infiltration processes in the construction and future operation stages.

Natural crustal earthquakes happen when preexisting faults have sudden movement. For induced seismicity of a low magnitude, the study of sudden failure of rock joints has more practical significance in engineering projects. Rock-like samples with five different undulations on artificial joints are tested by a split Hopkinson pressure bar (SHPB) to analyze the influence of joint undulation on dynamic failure strength and fracturing behavior. The rupture process is recorded by a high-speed camera using digital image correlation technology. Experimental results indicate that optimal undulation ranges in 50/120 to 50/140 have the maximum compressive strength and can absorb the most energy. The energy is absorbed by the concave structure rather than creating new cracks. Compressive failure tends to occur on the concave side and the concave side always has more fracture than the convex side. The degree of fragmentation decreased when the sample had higher undulation under the same impact velocity. The number of cracks and the size of broken blocks are determined by impact velocity. This research provides a beneficial attempt to understand the induced seismicity caused by a joint failure under impact load and is of great importance in mitigating anthropogenic geohazards economically and efficiently.

Urban sinkholes can cause subsidence damage to transportation infrastructures, demolition of buildings, and even the loss of human lives when they occur in a rapid way. In this study, the spatial distribution and the susceptibility mapping of the urban sinkholes were studied through the utilization of geographical information systems (GIS) with a sinkhole inventory and a spatial database that contains information on the geology, hydrogeology, and land use. Initially, 1155 sinkhole records from 2016 to 2019 were identified in Shenzhen. It reveals that the urban sinkholes mainly occurred in fill soil areas by examining the 3D geological model produced for this study, and it can also be easily triggered by heavy rains. Then, the sinkhole susceptibility map was obtained based on the gray correlation analysis (GRA). The sinkhole density map and the land subsidence Interferometric Synthetic Aperture Radar (InSAR) data in Futian District were finally used to verify the reliability of the sinkhole susceptibility map. The proposed spatial distribution pattern and the susceptibility mapping based on the GRA method demonstrate a promise to mitigating the risk of urban sinkholes.

In Japanese cities, the railway is an important means of transportation that is indispensable for people’s daily lives and economic activities. In the Tokyo metropolitan area, travel by rail accounts for about 30 percent of all modes of transport. But railways pose a major challenge to improving urban safety and ensuring the smooth flow of traffic, with accidents and traffic congestion occurring at level crossings where railway lines and roads intersect. Railways also have a major impact on city design by separating built-up areas. To address these challenges, initiatives are underway to move railway tracks on the surface to spaces underground for the removal of level crossings and the creation of seamless urban areas. This paper introduces projects underway in Japan’s cities to move railways underground.

With the continuous improvement of China's urbanization, the high-rise buildings, subways, large commercial complexes, and other projects are increasing, and the involved deep foundation pit engineering is also growing. Meanwhile, due to the sensitive geological environment and complex traffic conditions, the deep foundation pit project in urban areas faces higher technical challenges and construction risks, especially in soft soil areas. In this paper, a complex deep foundation pit group is analyzed by the numerical simulation, and different construction time sequence schemes of the foundation pit group are considered to study the differences in coupling effect on the lateral wall deflection, basal heave de-formation, and internal support axial force. Finally, some suggestions are put forward for the monitoring and construction of this project.

In 2018, Tokyo Midtown Hibiya was completed and opened in Hibiya, Tokyo. This is a large-scale complex urban redevelopment project in central Tokyo. At this time, the underground passage outside the site of the project and the underground square in the site were prepared. This has dramatically improved the dynamics of moving lines, which were conventionally vulnerable when crossing over subways. Tokyo is a city which rapidly became urbanized after World War II. The utilization of underground spaces is effective, but the space cannot be afforded in the progress of urbanization. This paper introduces Tokyo Midtown Hibiya as a good example showing the Win–Win situation between urban developments and underground space creation.

Taking the construction of the composite shield tunnel of Suzhou (China) Rail Transit Line 8 as an example, the reinforcement range of the overlapped shield launching end is calculated by Japanese elastic thin plate theory, static theory and slip instability theory, respectively. The finite element modeling analysis is used to obtain the soil displacement curve of the shield launching end in different reinforcement ranges, and then the simulation results are compared with the engineering-measured data. In the engineering example, the reinforcement area is 13.75 m wide and 6 m long. The three construction techniques of triaxial mixing, TRD wall forming and MJS all-round jetting are combined to fully ensure the quality of foundation reinforcement. The longitudinal reinforcement length calculated by the slip instability theory is similar to the longitudinal reinforcement length determined by simulation analysis and engineering measurement. The slip instability theory can be used to preliminarily determine the reasonable reinforcement range of the starting end of the overlapped shield.

The dynamic stress concentration ascribed to the scattering of stress waves encountering underground structures is an important factor affecting the damage of deep rock mass. A theoretical model was established in order to investigate the distribution of dynamic stress around a water diversion tunnel subjected to cylindrical P-wave resulting from near-field disturbance such as neighboring tunnel excavation and explosion in this study. Moreover, based on the steady-state solution of the wave function expansion method, the transient response around a circular lined tunnel with fully filled fluid subjected to half a sin wave with different incident times was derived. The calculation results indicate that waveform parameters, distance from disturbance source, lining thickness, and elastic modulus of lining materials have different degree effects on the distribution of dynamic stress concentration factor (DSCF) in rock and lining. Due to the presence of fluid, the distribution of DSCF would result in fluctuation phenomena when the wave number is large.

Acid fracturing has become an important tool for reservoir transformation. With the complex spatial morphology and high heterogeneity of the deep fractured-vuggy carbonate reservoir, it is difficult to develop it effectively. In this paper, indoor true triaxial acid fracturing simulation experiments and 3D scanning were carried out to analyze the acid fracture propagation morphology and study the process of crack propagation. Rock mechanical parameters were tested to indicate the degree of rock strength deterioration at different locations. The experimental results show (1) The acid fracturing affects the mechanical properties of the formation around the fracture, Young's modulus, and Poisson’s ratio of the rock around the wellbore decreased by 34.42 and 18.18%, respectively. The degree of acid corrosion at the distal end gradually decreased. (2) Natural fractures affect acid fracturing significantly. (3) Compared to the single acid injection construction, fatigue acid fracturing reduces the fracture pressure by 18.75%, and the fracture propagation pattern is more complex.

With the increasing depth of underground resource extraction and underground space exploitation, rock characteristics and confining stress conditions have changed, which brings a serious challenge for mechanized excavation, such as heavy wear on cutters, serious dust pollution, and significant decline in mining efficiency. It leads to a substantial increase in the cost of mechanized excavation operation. Rock fragmentation mechanism is the core content for optimizing cutter design and improving mechanized excavation efficiency. Resulting from the discontinuity damage of the rock under the cutter action, Discrete Element Method (DEM) has become one of the effective methods to study the rock fragmentation mechanism. A conical pick cutter is a typical mechanized rock-cutting tool. In this study, a two-dimensional discrete element model for rock fragmentation using a conical pick was established to simulate the fragmentation performance of the rock under different confining stresses. The change of cutter force during the cutting process was monitored and recorded, as well as the volume of broken rock. Finally, by calculating and analyzing specific energy under different confining stress conditions, the optimal working state was explored to make the rock-cutting specific energy lowest. This study explores the influence of confining stress on rock cutting and reveals the rock fragmentation mechanism under confining stress.

Microwave-assisted mechanical breakage of hard rocks is a promising alternative to drill and blast, especially in areas with stringent environmental protection regulations. Past research focused on numerical and laboratory studies on the change in the physical and mechanical properties of rocks, primarily using multi-mode microwave cavities. For the research using open-ended microwave applicators in fracturing large pieces of rocks, the 3D damage zone of one irradiation can be characterized. However, those research falls short in examining the interaction between different irradiations, i.e. how does the distance between two irradiations affect the interaction between the fractures? Using a customized open-ended microwave antenna and large rock blocks, this paper experimentally investigates the fracture interactions between two irradiations when different irradiation spacings are adopted. From the test results, the optimal irradiation spacing is determined. The finding of the paper provides a fundamental basis for the design of the irradiation pattern when the technique is commercially used in the field.

Deep-buried tunnels in mountainous areas often lack seismic protection except when crossing faults. However, tunnels crossing abrupt transitions of soft and hard rock strata can suffer significant seismic damage during strong earthquakes. Hence, it is crucial to study the seismic safety of such tunnels. This study compares the structural forces of the tunnel crossing soft and hard rock strata, homogeneous hard rock, and homogeneous soft rock during strong earthquakes. It analyzes and evaluates the dynamic response characteristics and seismic safety of the tunnel under these conditions. The results indicate that the tunnel’s lateral safety is highest when crossing homogeneous hard rock, followed by soft hard rock and homogeneous soft rock. As the distance from the soft and hard rock interface increases, the tunnel's transverse and longitudinal stress safety becomes more like that of the corresponding homogeneous rock. Seismic damage can occur near the soft-hard interfaces due to longitudinal internal forces, with some contribution from transverse internal forces.

Using the Lame equation and the three-parameter viscoelastic foundation model, the solution of time-dependent ground settlement induced by displacement of the retaining wall was derived. Based on a 30.2 m ultra-deep foundation pit in Hangzhou soft clay, the solution was validated. The results indicate that (1) The creep will induce ground settlement that does not depend on the extra displacement of the retaining wall, which not only causes the ratio of the maximum ground settlement (wm) to the maximum displacement of retaining wall (dm) during excavation to be much greater than that of non-soft clay foundation pit, but also causes the continuous ground settlement during basement construction. (2) The ground settlement induced by creep increases with the displacement of a multi-strutted wall, showing a concave settlement mode. (3) wm/dm is primarily affected by the creep characteristics of soft clay and the construction time, and seems independent of the displacement of the retaining wall.

Understanding the ground response induced by underground excavation in granular soils is important for assessing the construction risk in similar urban geological environment. This paper presents an application of the hierarchical FEM/DEM coupling multiscale approach in the simulation of classical trapdoor tests. The multiscale simulation reveals the development pattern of the soil deformation, soil shear zones, and load transfer in the case of various overburden depths and soil density. Furthermore, the multiscale approach provides insight into the microstructure evolution underlying the macroscopic deformation from the perspective of RVE powered by DEM. This study demonstrates that the multiscale approach can bypass the phenomenological assumptions on conventional constitutive relations and accurately reproduce the soil arching behavior due to underground loss. Meanwhile, based on the efficiency advantage of massively parallel computation, the multiscale approach is expected to further solve the engineering-scale problems under complex boundaries.

This paper proposes an automated deep learning (AutoDL) framework for the dynamic driving attitude prediction of the tunnel boring machine (TBM) in tunnel construction. A standard process is proposed for the automated deep learning framework, including data preprocessing, optimal hyperparameter tuning, algorithm selection, and model performance evaluation, which can intelligently learn the time-varying monitoring data collected by the smart sensors installed on TBM. Moreover, a prediction interval is carefully designed to well consider the uncertainty, which is stable enough to raise the reliability of the prediction results. To validate the effectiveness and practicability of the proposed approach, it is applied in a TBM project for a natural gas pipeline network in Chongming Island–Changxing Island–Pudong New Area in Shanghai. Results indicate that the proposed automated deep learning with particle swarm optimization (PSO) algorithm greatly reduces the requirements of model training evaluation on the professional knowledge of developers, which can return not only high-accuracy predictions, but also interval-based predictions considering uncertainties. As for the engineering practice value, the deviation of TBM driving attitude in each segment ring can be dynamically and reliably estimated, which provides valuable evidence for managers to timely adjust the TBM operation to ensure the project quality.

This paper is concerned with the preliminary application of a non-probabilistic tool, called an Info-Gap method (IGM), to the stability design under severe uncertainty for coping with the spalling property in the hard rock tunnel. Such a tool for the reliability-based design of tunnel stability having severe uncertainty is illustrated non-probabilistically on the basis of a deterministic mechanical model involving the slab-strip failure caused by the surrounding hard rock spalling. In the presented IGM, the non-probabilistic reliability analysis was explored, which elaborates how the Info-Gap modelling can be employed, and then how the reliability can be assessed non-probabilistically with the aid of the robustness function. On this basis, one type of reliability-based design chart relating the thickness of a single slab-strip to the spalling property of the chosen hard rock tunnel example was developed. This proposed non-probabilistic IGM can make the reliability-based design in the tunnel community have a possibility to be conducted when the probabilistic representation of uncertainty seems to be difficult due to extremely insufficient information.

The paper deals with the proposed development of a mountainous tunnel in the Tzoumerka area in Greece that can facilitate ease of access between the villages of Melisosurgoi and Theodoriana. These two settlements are currently at the end of the mountainous ring road and although positioned 10 km apart, a travel time of almost 2.5 h is required to reach them. The design aspects in terms of tunnel alignment, geometrical and cross-sectional characteristics, and support requirements are presented, along with the projected cost estimations. Yet, the paper is focused on assessing the feasibility of the project not only taking into account mere financial terms, but also considering—besides the construction costs—all other benefits attained by the development of the road tunnel which are related with the drastic minimisation of the travel distance and time between the two villages and all other settlements in the wider area. The above framework provides all the required data to directly compare the development costs along with all the direct and indirect benefits related to the socio-economic environment to be developed affecting the communities in the area, throughout the whole life-cycle of the project.

The cross-section shape of deep tunnels may be complex, e.g., horseshoes, semi-rectangles, rectangles, and arch-wall; and the surrounding medium of them may have complex properties. In order to obtain seismic responses of deep tunnels in these complex conditions, a unified analytical solution is proposed. The ground-liner interaction can be no-slip and full-slip, and voids behind the liner are considered. Moreover, the ground anisotropy, as well as the drained and undrained loadings are considered. The unified analytical solution can be used to obtain stresses and displacements of deep tunnels with arbitrary shapes, in various ground conditions, and with different ground-liner interactions. The complex function theory and the conformal mapping technique are employed to develop the solution. The results from the proposed analytical solution show that the cross-section shape and the incident angle have a significant impact on the seismic performance of deep tunnels.

As large-scale urbanization continues to unfold globally and urban populations rapidly rise, the development direction and form of urban space have become hotly debated topics. This study combines the national first prize-winning entry from Milan Design Week and proposes a new perspective on urban development, which takes the form of “giant constructions” using an algorithmic generating method. The research attempts to use urban vitality points to generate a group of giant constructions and create a new urban upper space through a huge arch system that does not conflict with the existing urban space. On top of this, Chinese bracket arch elements are extracted to generate modular building units within the giant constructions. The urban solution proposed in this study forms an aerial community consisting of clusters of buildings and open space, providing a large amount of vertical green space and living space in urban airspace to solve the problems of insufficient central green space and commuter housing. It resolves the limitations of urban space and enhances disaster resistance, providing new ideas for reshaping urban space and achieving green sustainability.

After the incremental wave of rapid urbanisation, managers, designers and users have to face the re-evaluation of spatial quality and spatial vitality. In the era of stock renewal, the multiplicity of road forms and the vitality of road space have brought greater challenges to the problems of stock development and urban renewal and triggered the academic community to pay attention to the rational use of public space around elevated. Elevated bridges are an important result of incremental planning, and the comfort of space is an important practice to meet the demand of stock planning. In this paper, we extract a typicalised scenario of urban elevated space, and simulate the impact of urban elevated on the thermal comfort of the surrounding public space through environmental diversity maps. At the same time, we investigate the use of eye-tracking and SD evaluation methods to construct a perceptual evaluation system for public spaces around elevated spaces. The goal of this study is to make a scientific exploration for enhancing the vitality of elevated peripheral public space, and also to provide a reference for the future development of cities towards elevated spaces.

Addressing issues of urban congestion and limited activity space, this study probes the potential of vertical transport and elevated city designs. Our novel methodology seeks a deeper comprehension of societal expectations for future cityscapes. We examine cinematic and televisual portrayals of future cities, sifting through their conceptual frameworks. Harnessing semantic segmentation technology and AI-facilitated diffusion model generation, we analyze current urban scenarios to extract pertinent spatial and design elements. Subsequently, we develop tailored elevated city transformation proposals to further understand societal desires for future urban streets. Employing interdisciplinary approaches, we identify key public interests in envisioned urban settings, proposing relevant transformation plans based on current case studies. This pioneering research is set to significantly contribute to the shaping of future urban environments, offering crucial insights for urban spatial conceptualization.

The flow channeling effect is a well-known phenomenon in fractured rock masses, which has been intensively investigated for many years now, for various purposes and under different practical engineering backgrounds. Though it has remarkable impact on the exploitation of geothermal energy through fractured reservoir as well, there lacks systematic quantitative analysis on its influence. In the present work, we developed a series of general fracture networks with randomly distributed apertures and special fracture networks with artificial dominant flow paths (with some fracture networks of uniform fracture apertures as the base case), then we conducted conjugate heat transfer analysis considering heat recovery from rock formation in practical scenarios. Preliminary results show that the impact of channeling effect on the overall heat recovery capacity of a reservoir won’t take effect before a threshold injection flow rate, and the associated impact would enhance with increasing flow rates and the mean apertures of all fractures in the channeling flow path. What’s more, it’s not the case that the heat extraction performance of a reservoir would be weakened, as only those flow paths with limited heat supplements are harmful. Therefore, we also seek ways to detect those paths and try to eliminate their impact.

Among the various heat transfer elements, heat pipes are currently one of the world's most efficient, allowing large amounts of heat to be transferred from one end to the farther end quickly and without any external forces through a small cross-sectional area. Using heat pipes in geothermal energy utilization allows a broader range of high-temperature surrounding rocks to be thermally activated, and the efficiency of geothermal energy extraction can be improved. In this paper, a numerical model is established to analyze the effects of different heat pipe arrangements and degrees of clustering on the heat exchange, then the temperature variation is explained by the thermal activation distance and the amount of heat transfer area loss. It is concluded that (i) heat pipes can effectively increase the heat exchange capacity of the lane, and laying a row of heat pipes increases the temperature difference between inlet and outlet water by 25% at maximum; (ii) inclined heat pipes have more minor heat exchange area loss and more substantial heat exchange capacity; (iii) heat pipe clusters received a maximum temperature increase of 156.25%, and when the number of heat pipes used is more than or equal to 5, attention should be paid to the way of arrangement to ensure that the average heat transfer area of heat pipes is more significant than 0.6 m2 to give full play to the heat transfer capacity of heat pipes.

The use of underground spaces for renewable energy production and storage has gained increasing attention as a strategy for making cities more sustainable. Underground spaces offer several advantages for energy production and storage, including insulation properties, thermal stability, and relatively low environmental impact. This paper explores the potential of underground spaces for renewable energy production and storage and highlights some promising examples and case studies. In addition to renewable energy production, underground spaces can also be used as storage facilities for renewable energy. One promising technology is underground pumped hydro storage. Another promising technology is compressed air energy storage (CAES), which involves compressing air into underground caverns or other spaces during periods of low energy demand and then releasing the air through turbines to generate electricity during periods of high demand. The SubSpace Energy Hub initiative that was created in June 2022 in the Hagerbach Test Gallery in Switzerland offers a platform for the development, prototyping, and installation of new technologies that promote best practices in sustainable energy use and storage. The aim is to be a model ecosystem of sustainable energy storage and delivery in support of green energy use in future cities. While there are still challenges to be overcome, such as the relatively high cost of some underground technologies and the need for appropriate regulatory frameworks, the examples and case studies outlined in this article demonstrate that there is already progress being made toward creating more sustainable cities using underground spaces.

Large-scale long linear engineering (LLE) projects have the characteristics of difficult coordination, challenging progress control, frequent changes, extensive archives, and difficult transfer. Engineering management (EM) faces many highly complex and fragmented information problems, making the need for digitalization even more urgent. This article proposes a DT model suitable for the management of LLE such as highways. By using long-endurance and high-precision UAV oblique photography technology combined with BIM, GIS, and IoT technology integration to build DT space, the project management digitalization based on DT was realized in the Nantong Ring Expressway project. The practical results show that: 1. DT-based engineering project management can achieve autonomous identification and warning of project progress, as well as automatic quantity calculation, improving the efficiency of project management; 2. DTs have improved the refinement, standardization, and real-time level of engineering project management while achieving the value regeneration of digital assets for highways. Finally, this article summarizes the problems and practical experience faced by DTs in engineering project management.

Clarifying the point cloud distribution is the basis for the correct use of point clouds. A method is proposed to characterize the point cloud distribution using point cloud spacing and thickness. The point cloud spacing is decomposed into point spacing and ring spacing. The point cloud coordinate, spacing, and thickness formula are derived sequentially from Terrestrial laser scanning (TLS) rotation mode, tunnel geometry, and measurement error. And the effect of measurement conditions, such as TLS resolution, linearity error, and tunnel diameter, on the point cloud distribution is discussed. The resolution is positively correlated with the point cloud spacing and enhanced with the increase of scanning range, but not with the point cloud thickness; the linearity error is positively correlated with the point cloud thickness but weakened with the increase of scanning range and not with the point cloud spacing. The effect of tunnel diameter on point cloud spacing is similar to that of resolution, while the effect on point cloud thickness is close to that of linear error. Theoretical methods are used to quantitatively describe the point cloud distribution so that the point cloud can be understood and applied from the perspective of the point cloud generation principle. The effect of measurement conditions on the point cloud distribution provides a reference for the design of tunnel monitoring schemes.

Tunneling projects frequently encounter intricate geological conditions during excavation. A comprehensive understanding of subsurface geology is imperative for tunnel design. This research introduces a novel shield tunneling construction simulation methodology within a three-dimensional (3D) geological model based on an improved coupled Markov chain. The improved Markov chain method enhances the alignment of the predictive output with the probable stratigraphic distribution. This study marries engineering geological survey data with the shield tunneling excavation simulation. To establish a congruent relationship between the regular grids of the geological model and the irregular grids of the numerical model, an asymmetric grid 3D mapping technique is proposed. The development degree of unfavorable weak interlayers impacting tunnel construction is evaluated through the defined exceedance probability. In light of these premises, the simulation methodology is applied to the detailed modeling of a large-diameter undersea tunnel in Qingdao. Based on the most unfavorable weak interlayer development scenario, the safety performance of a 3D shield tunnel traversing this stratum is analyzed using numerical simulation methods. The promising potential of the proposed methodology for tunnel excavation simulations under geological uncertainty is validated. The approach offers an innovative contribution to the field, enhancing tunneling predictability, risk management, and overall construction efficiency.

The geotechnical characteristics of strata are crucial indicators for conducting subterranean engineering surveys and designs in the development of underground space engineering. This paper has developed a monitoring system while drilling and suggested a set of intelligent data processing schemes to address the current issues of low automation, inadequate utilization of borehole data, and challenges in identifying the lithology of the stratigraphic interface in the drilling process of engineering survey. On-site tests were conducted in Chongqing City and Guangdong Province, China, and a large amount of effective borehole data was obtained and extracted. The particle swarm optimization (PSO) algorithm was used to optimize the parameters of the kernel function based on the support vector machine (SVM) algorithm in order to deliver the best learning and prediction outcomes. The PSO-SVM algorithm was utilized to identify the key lithologies of the stratum and to predict the uniaxial compressive strength of the rock mass. The performance shows that the prediction results are in reasonable accordance with the on-site lithology catalog and laboratory mechanical test records, and PSO-SVM is excellent in identifying the critical lithology of the stratum and predicting the critical parameters of the rock mass.

The underground pedestrian network of the Otemachi-Marunouchi-Yurakucho district has been reinforced through developments since the 1980s. This infrastructure disperses pedestrian congestion above ground. Furthermore, underground pedestrian spaces are indispensable infrastructure for barrier-free access, such as commuting in a wheelchair or shopping while walking with a stroller. However, when walking through underground pedestrian spaces, one can observe its labyrinthine complexity. This paper outlines how we collected, maintained, and disseminated data on underground pedestrian spaces.

Accurately predicting cutter wear is critical when budgeting construction schedules and costs for tunneling projects involving tunnel boring machines (TBMs). To address this need, the cutter life index (CLI), developed by the Norwegian University of Science and Technology (NTNU), is usually calculated using Sievers’ J-value (SJ) and the Abrasion Value Steel (AVS). However, measuring the CLI is challenging owing to the need for specialized test equipment, as well as the time-consuming and complex nature of the experimental process. This study aims to estimate CLI values based on common mechanical rock properties and the Cerchar Abrasiveness Index (CAI). The considered mechanical rock properties include the uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), equivalent quartz content (EQC), and brittleness indices (B1–B5), as well as the cohesion derived as a function of uniaxial compressive and Brazilian tensile strengths. To develop an estimation model, we used linear regression analysis and various machine learning techniques, including extreme gradient boosting (XGBoost), extra trees (ET), gradient boosting machines (GBM), random forests (RF), decision trees (DT), and adaptive boosting (AdaBoost). For the linear regression, CAI, EQC, BTS, and the rock type were defined as the input variables, taking multicollinearity into account. For the machine learning models, appropriate input variables were selected. A literature survey was conducted to compile a suitable dataset, which was then divided into 80% training data and 20% test data. The accuracy of the predictive model was evaluated using the Root Mean Squared Error (RMSE) and coefficient of determination (R2) of five k-fold cross-validation values and considering the skewness of the data. The results show that the gradient boosting machine model provides the best predictive performance, with an R2 of 0.93, 0.70, and 0.89 for the training, test, and entire datasets, respectively.

Tunnel Boring Machines (TBM) are primarily used for the excavation of metro tunnels in urban areas, as they can achieve almost zero disturbance to the surrounding rock mass and can attain high advance rates. Modeling the penetration rate (PR) of a TBM is an important aspect of any tunnel excavation, as its more accurate prediction impacts the overall construction cost, and the potential delay of the tunnel delivery to the society but also can provide insights of upcoming safety issues. This paper deals with the prediction of the PR with Machine Learning (ML) methods utilizing data coming from part of the construction of Athens metro Line 2. The data consists of the TBM data, provided by Attiko Metro. By using an Earth Pressure Balance-Tunnel Boring Machine (EPB-TBM), it is possible to balance the pressure conditions at the tunnel face, avoiding face collapse and controlling ground settlements. A solitary analysis of just the machine parameters without any additional information (geological, geometrical, etc.) can derive meaningful information regarding the quality and quantity effects the additional information e.g., geological medium has on a tunnel excavation when using an EPB-TBM. Two ML models (Extreme Gradient Boosting Regression—XGBR, Artificial Neural Networks—ANN) were developed and compared between them utilizing a set of input parameters derived from a feature importance analysis. The results show promising results having a consistent behavior across almost the entire range of the test dataset used, closely following the trend and behavior of the actual PR.

The impact of complex geology on engineering excavations in modern urban construction is a topic of great interest, and modeling is a critical tool for assessing this impact. Despite the availability of information modeling tools for storing geological information and refined numerical analysis software, coupling these two types of tools to build computational models that effectively analyze the impact of geological information on engineering excavations remains challenging. This often results in critical geological information being underutilized or overlooked in the simplified process of adapting computational time and resources. This study proposes a model mapping algorithm based on the interpolation framework of numerical manifold method (NMM) that can seamlessly integrate complex geological information from a 3D geological model established by borehole big data into the numerical calculation. The algorithm's robustness is examined in terms of the spatial distribution mapping of strata and the abrupt distribution mapping of mechanical parameters. The study then discusses the influence of spatial variability of geotechnical property on the spatial effects of excavation, and verifies the effectiveness of the algorithm by comparing it with actual engineering monitoring data. The proposed algorithm can provide a refined numerical service for pre-planning underground spaces and for safety assessments during construction, effectively assessing the impact of complex geology on engineering excavations.

Due to the inherent limitations of underground space, such as lack of connectivity with the aboveground environment, natural ventilation, and sunlight, underground space occupants tend to face more health risks than their aboveground counterparts. Greenery has been identified as one of the key elements fostering underground occupants’ health. However, it remains unclear whether different types of greenery have differential effects on occupants in underground space. This study thus aims to investigate the impacts of different types of greenery on underground occupants’ psychophysiological health and cognitive performance through virtual reality (VR). Four scenes (i.e., 2D green wallpaper, individual 3D plants, 3D plant wall, and no greenery) were created in virtual models. Thirty-two subjects were recruited, and randomly separated into four groups. During the experiment, subjects were required to complete four cognitive tests. Meanwhile, their psychophysiological states were measured using the indicators of heart rates and skin temperatures. Paired t-tests and Wilcoxon signed-rank tests were adopted to compare subjects’ health conditions before and during the cognitive tests. ANOVA and Kruskal-Wallis tests were applied to conduct inter-group comparisons. The cognitive tests have resulted in a significant increase in psychophysiological stress among subjects in the non-green scene (p<0.05), which proved the validity of the experiment setting. The results indicated that: i) greenery did not have significant impacts on underground space occupants’ cognitive performance; ii) all three types of greenery could alleviate the stress of underground space occupants; and iii) there was no significant difference regarding the alleviating effect among the three greenery groups. The findings imply that, from the perspective of underground space occupants’ health, types of greenery do not make a significant difference. Taking design and maintenance costs into consideration, 2D green wallpaper could be the most efficient option among the three covered in this study.

In this paper, a novel sensor using low-cost parts was designed and its capability was evaluated to be used efficiently for inclination and displacement monitoring in the field. Robust sensor design was employed ensuring strength and resistance to water and severe weather conditions. The proposed monitoring system consists of the inclination sensor interconnected to a Raspberry Pi microcomputer with a LAN or Wi-Fi connection. Sensor acceleration and inclination accuracy were achieved using Complementary or Kalman Filters and evaluated during shaking table and flexural laboratory tests when put alongside high-performance high-cost sensors. Data transmission was achieved in real-time using the LabVIEW programming environment with online view capabilities.

In recent years, urban construction and management have entered a new era of intelligence. BIM technology has become one of the crucial technologies for the entire life cycle process of planning, designing, constructing, and operating in urban underground space facility (UUSF). However, the current UUSF standards still lack a unified coding system based on the entire life cycle of the facility. This lack results in difficulties for facility data to be interconnected in the BIM environment. This paper examines the coding research results of related industries both in China and internationally. Based on Omniclass, a classification and coding system for UUSFs is proposed. The existing UUSF coding standards are also combined with Omniclass to establish mapping rules between Omniclass and existing coding. This results in a set of methods for coding UUSFs based on Omniclass. Coding examples of some facilities are also provided in the paper. The coding method proposed in this paper can provide theoretical support for the application of UUSF data in the BIM environment. It facilitates the efficient transmission of underground space data in the entire life cycle of UUSFs.

Safety is one of the most critical parameters in an underground project. A typical example of such an underground project is the METRO, which is an integral part of the daily lives of millions of citizens and the study for an effective security plan is of high importance. The organized evacuation during an emergency contributes in reducing the overall risk. Evacuation simulation models take into account several parameters and contribute significantly in developing an effective evacuation plan, however, they fail to consider the actual behavior of people, and engineers make assumptions when conducting the simulations. In the current study, a Virtual Reality (VR) application is developed to assess people’s behavior in a METRO station evacuation. According to the scenario, they have to evacuate a platform in which a fire occurs. For each participant, the time, the exit route choice, and the distance traveled are recorded. The experiment resulted in a safe evacuation for all users. The high variation of exit route choice and the VR application enable the evacuation to be simulated with a high degree of realism and in a safe environment.

Exploration and utilization of urban underground space require a sound understanding of subsurface stratigraphy. Image-based machine learning algorithms are appealing to engineering practitioners as they can effectively leverage valuable geological knowledge reflected in training images for stochastic simulations. However, in practice, only limited training images are available, which may not exhaust all the potential stratigraphic patterns at the site of interest. To explicitly tackle this dilemma, in this study, a generative adversarial network (GAN) is employed to generate multiple random image samples from a single training image. The compatibility of generated image samples with site-specific data is ranked based on total information entropy, and the selected image samples can be used to derive a robustness index for adaptive specification of the optimal next sampling location. The performance of the method is demonstrated using real examples from a Hong Kong reclamation site. Results indicate that the proposed framework can efficiently generate multiple image samples with plausible geological patterns, and the adaptively selected training images can improve the stochastic prediction performance.

Urban development in China has been facing various challenges in recent years. Scenario planning is considered a practical approach to enhance a city’s adaptability to the changes in public service and market demand in the future, as well as to support decision-making. The author chose the case of underground space planning on Hengli Island, Nansha in the Greater Bay Area of China to explain the mechanism of how scenario planning is applied in underground space development, including setting objectives, formulating strategies, and proposing underground space planning schemes to re-distribute spatial resource more flexibly and efficiently, ensure resilience, and achieve sustainability in the future.

The planning and design concept of underground space is comprehensively introduced, combined with the construction of underground public parking lot in Zhumadian business center. Firstly, the importance of the introduction of underground traffic is focused on, aiming at the problems currently encountered in the area. Secondly, the overall design scheme of underground space is introduced. Finally, to alleviate local financial pressure, the scheme of one-time planning but phased construction and batch operation is put forward. The completed part of each phase with independent functions put into operation and reserved interfaces. Promote by stages, gradually improve the functions, and finally build an integrated underground space with complete functions. The construction scheme breaks the irreversibility of underground space construction, a new idea for the development of large-scale underground spaces under limited funding conditions has been proposed through clever engineering staging, which can provide a reference for similar projects.

The Beijing Sub-Center Station is a large-scale underground transportation hub, located in the core area of Beijing Sub-Center by the Grand Canal. The total construction area of the hub is approximately 1.28 million square meters, with a total depth of about 30 m. The underground space will focus on the transportation function of the hub, while the above-ground area will form a highly concentrated financial & business area. This paper, based on the underground space planning of the Beijing Sub-Center Station, will systematically discuss the comprehensive planning strategies of the underground space concerning six main aspects, that is the ecological adaptability of the station, the establishment of an efficient transport system, the continuous pedestrian network, the integration of underground facilities, the economic value of the underground space and the application of new technologies to improve the underground resilience. The planning strategies in response to these key issues will provide useful reference for the integrated development of the transportation hub area and improve the overall operational efficiency of the urban region.

This research focuses on the short and long-term sustainability impacts that new mass-transit projects have on urban areas. In current practice, sustainability is primarily focused on construction and operation phases through the introduction of more sustainable constructional and operational methods, equipment, and materials. There is no sustainability-specific research dedicated to the pre-construction phase. Analysis of Canadian and Netherlands mass-transits outlines that infrastructure delivery timelines, particularly, pre-construction periods are on the rise. The non-accounted pre-construction sustainability impacts may trigger incorrect designs, constructions, and operations. As seen worldwide, the relatively cheaper “at-grade”, “above grade”, and “cut and cover” construction methods are frequently prioritized over the relatively more expensive “tunnelling”. Using a novel methodology allows coherent selection of the best for the environment, society, and economy, and thus, the most sustainable infrastructure (Kondrachova et al. in University of Toronto Mississauga rapid transit connection concept, 2022 [1]), the pre-construction planning can be optimized. Such optimization will help to reduce the pre-construction timelines and thus, to improve the sustainability of each new infrastructure toward more sustainable future urbanization.

Underground space development has demonstrated more prominent advantages than surface space development. Qingdao, an eastern coastal city of China with unique geographical characteristics, plays a significant role in national spatial economic allocation. Since the twenty-first century, the developing-utilization of urban underground space in Qingdao has entered a high-speed development period. A networked and multi-core underground space is basically formed in the central urban area. The underground space planning of Qingdao proposes that “underground Qingdao” will be mostly completed by 2050. Therefore, this paper summarizes the current development status and the traffic facility, municipal infrastructure, comprehensive development and technology of underground space in Qingdao. Moreover, by investigating the current problems of underground space development and utilization in Qingdao, combined with the goals and strategies for future development, we propose future development suggestions. Promoting the construction of a conservation-minded city and realizing sustainable and healthy development in Qingdao is of great significance.

Since China’s reform and opening-up, expanding urban areas has been mainstreaming to meet the demands of society in the face of rapid urbanization. Many of these contemporary new districts still face common urban problems such as disorderly land construction, negative built environment, and severe traffic congestion. Against this backdrop, the underground space presents a valuable urban resource that can significantly influence sustainable urban development and alleviate complex urban issues. To illustrate this point, this paper examines the case study of Jinan sub-central city, covering an area of approximately 35 km2. This paper will generalize the Chinese modern garden city concept and integrate it into the preparation of objectives, methods, schemes, and construction modes, establishing the green, ecological, and sustainable underground space in the new district. These advanced concepts and practice work from the case study will provide potential support and assistants for the future underground space construction in new districts.

Recreational business districts (RBDs) are often designated as the new growing point of metropolises upon sustainable development. Being a key component of a resort area and also a regional public service center, an RBD can face problems in spatial capacity and functional arrangement. In this context, it is essential that the use of underground space be involved and planned presciently. Through the case study of the South Parcel of Shanghai International Resort, which is also expected to serve as a city sub-center, this paper discusses key issues that drive the underground space use in RBDs and raises and expounds three main planning strategies for underground space. The findings of this study can provide insight into underground space planning in similar areas.

This paper aims to address the problems associated with urban last-mile delivery and studies the last-mile delivery system of underground logistics for urban areas in light of the trend of intelligent development. Based on factors such as population size, development level of intelligent technology, and logistics delivery service level, the intelligent last-mile delivery system is divided into multiple level, and a last-mile delivery system based on intelligent level for underground logistics is proposed. Finally, taking the Jinan Prior Zone in China as an example, a case study for last-mile delivery of underground logistics is proposed and illustrates the progressive enhancement of the system from an Intelligent Level One to an Intelligent Level Three delivery framework.

Although cities occupy only about 2% of the land surface, they consume approximately 70% of the world’s resources and energy and emit 70% of the world's greenhouse gas (GHG) emissions. Carbon–neutral development goals have already been established in more than 400 cities and organizations, and China has set the goal of reaching a carbon peak before 2030 and achieving carbon neutrality by 2060. As a promising spatial resource, underground spaces in China can provide stable and sufficient spatial support for various emission reduction and sink enhancement measures, which are of great significance for achieving the goal of carbon–neutral development. This study aims to construct an implementation pathway and typical modes for underground spaces in China for a carbon–neutral city and provide theoretical guidance for carbon–neutral-oriented urban planning and urban underground space planning.

China has built the world’s largest high-speed railway network. The developed network has become a major driving force for high-quality development of cities, especially for the construction and development of the surrounding areas of station. This paper summarizes the new trends of station-city integration development in the stage of high-quality development, and its new requirements for urban space, including underground space, such as higher density, more three-dimensional and more intensive development. Combined with the practice of underground space planning in Hangzhouxi Station area, it proposes to take “building a new generation TOD4.0 benchmark, building an integrated, intensive, comfortable, intelligent and efficient underground space demonstration area in the station city” as the planning object. The needs and difficulties are evaluated from five aspects including function, vitality, traffic, municipal, administration and control, and planning strategies and layout schemes of various systems are formulated to consolidate the construction base of the core area. It aims at enhancing the attention to the underground development and utilization of station-city integration area, and providing a thinking path for its planning research.

By studying the experience of typical port renewal projects at home and abroad, this paper summarizes that port area renewal has the characteristics of prominent location advantages, large-scale land development, prominent contradiction between new large-scale development volume and end traffic location, and high quality requirements for waterfront landscape space. In view of these characteristics, combined with the underground space planning project of Qingdao Cruise Port, this paper proposes that the development and utilization of underground space in the renewal of port area should adopt the strategies of resilience and safety, three-dimensional transportation, dynamic space, municipal integration and overall development, and innovatively explore the implementation paths such as development alliance, layered transfer, and capital planning, so as to provide reference for the development of underground space in similar areas.

Hong Kong, one of the most densely populated places in the world, has a long history in utilizing sub-surface spaces for different types of uses. Most common examples include the railway, vehicular and pedestrian tunnels, shopping malls etc. With Hong Kong’s hilly terrain and good rock quality, the use of rock cavern has also gained popularity in the last 40 years but has been focusing to accommodate isolated government facilities with low human occupancy. With growing population and the aim to improve livability, cavern areas have been recognized as one of the land supply sources. The Hong Kong Government has injected major resources into the research and investigation to further unleash the potential of this land supply source. Land use planning and technical tools have been introduced throughout the years to facilitate cavern development. Uses of cavern is no longer an isolated development and planning for the use of these spaces is now part of the urban planning process, in particular for new town development. With technological advancement, a wider range of cavern uses has been made possible and an integrated planning approach to consider uses of surface, sub-surface and wider area is being adopted for district- or territorial-wide development. The Outline Zoning Plans formulated under the Town Planning Ordinance provide statutory controls on land use and development parameters at district and local levels. To facilitate the wider and more efficient use of caverns, this paper aims to provide a review on the existing land use zoning practice for cavern developments in Hong Kong. Relevant overseas cases will also be reviewed for best practice and latest trend. The objective is to examine the needs thus measures for enhancement to the zoning mechanism to further facilitate cavern development in Hong Kong.

Subway construction not only needs to meet the planning requirements of the respective areas but also plays a crucial role in urban renewal. The conventional TOD model with high-density development is not suitable for the spatial pattern and preservation requirements of historical and cultural street blocks. This paper takes Beijing Subway Line 19 Ping’anli Station as an example and proposes the basic design strategies for the development of underground spaces in historical street blocks using the acupuncture-style TOD model. The focus is on prioritizing quality and demand rather than increasing density and scale. This provides a reference for future updates of underground spaces in historical street blocks.

Urban Rail Transit Leftover Space refers to the structural space generated due to cost-saving considerations in deep underground stations or sections through a cut and cover method, where no backfilling is made. In response to high-quality urban development, utilizing such existing assets has great practical significance in improving the efficiency of urban land utilization, revitalizing idle assets, and supporting the construction of urban rail transit. This paper summarizes the engineering characteristics of these spaces, explores pain points in the development and construction process, and provides targeted countermeasures and suggestions. Finally, this paper proposes strategies for utilizing urban rail transit leftover spaces based on the Integrated Shared Corridor Project in Chengdu High-tech Industrial Development Zone, for reference.

Tokyo’s underground rail system is used by approximately 10 million people every day (2018) and is one of the few underground transit cities in the world. The large number of daily passengers is apparent when compared with New York at 5.6 million (2014) and Paris at 4.2 million (2011). In central Tokyo, rail transit accounts for 50% of all means of transportation. Compact cities centered on a station and human centered, walkable cities are promoted as policies of the Ministry of Land, Infrastructure, Transport and Tourism, with urban development linked to stations, bus terminals, and other transport infrastructure becoming increasingly important. Linking urban developments to transit infrastructure is challenging given that urban developers and transit operators are often separate entities with different development periods. Recently however urban developments linked to transit infrastructure have been advancing in the areas around Tokyo Station, Shibuya, and Toranomon. This paper addresses the significance and challenges of urban developments integrated with underground rail and infrastructure beginning with an exposition of the Toranomon Hills Station and Toranomon Hills Station Tower urban redevelopment projects in the Toranomon area.

A large number of studies have concluded that the agglomeration effect of rail station and urban street accessibility leads to enhanced public amenity. In particular, the effect is observed in above-ground and underground pedestrian networks in rail station precincts. Taking the Qian Hai area in Shenzhen as an example, a paper identified indicators of vitality in some above ground and underground pedestrian streets networks in a subway transit study subject area. The study then rated the vitality indicators and mapped it on a GIS platform. The platform facilitated spatial visualization of less-developed areas in the above ground and underground systems. This improves the ability of policy makers to make data driven decisions on prioritisation of public amenity and asset improvements.

The influence of cross mining tunnel on geothermal resource utilization in abandoned mines is that many mines are closed or abandoned, and the cross mining tunnel makes it possible to absorb and transfer geothermal energy resources over a wider area without hydraulic fracturing. In contrast, the mining tunnel closed during the operation phase due to ventilation, drainage design, or mining area requirements can be opened and merged into the main mining tunnel after the mine is abandoned to activate a larger area of high-temperature surrounding rocks. To explore the effect of interconnected cross-alley on geothermal resource utilization in abandoned mines, this paper establishes a numerical model to analyze the intersection angle and backwater parameters of connected alleyways, finds the gain effect of heat transfer under a slight angle, proposes the positive flow addition step (FPAS), and quantifies the misalignment symmetry phenomenon of each alleyway at the appropriate location. It is concluded that: (1) the interconnection of cross mining tunnels increases the inlet and outlet temperatures to 7.31–7.81 °C, an increase of 5.2–12.37% compared to the condition without cross mining tunnels; (2) the cross mining tunnels distributed in 0 ± 10°, 90 ± 50°, and 90° directions have a more significant gain effect on water temperature, and the positive flow addition step (FPAS) can quantify the gain effect of water temperature in the center. FPAS can quantify the temperature difference due to water flow direction on both sides of the centrally symmetric cross-alley; (3) when the number of cross-alley >1/150 m, the gain effect of increasing the number of cross-alley on temperature is no longer apparent, and the recharge flow rate of 750 m3/h is considered to be the cut-off value to produce the temperature difference change.

It is obvious that underground spaces successfully contribute to the creation of a sustainable and resilient urban environment, which is proven by many researches and case studies. The construction of such spaces, from the aspect of technical and technological requirements, has advanced greatly in the last thirty years. In contrast, the implementation of underground spaces in the planning framework and the very institutionalization of underground urbanism take place much more slowly. It is necessary to create the controversy of the cause of this phenomenon, by taking back a few steps to the time of the first ideas of planning underground urban spaces, thus reexamining the very concepts of implementing underground urbanism in planning processes. The author analyzes the current results achieved in the world of the subject matter, and the current legitimate planning processes of a developing country (Republic of Serbia), which is still planning to lay the foundations for efficient planning of underground urban spaces. The goal of the paper is not to criticize the existing models of implementing underground urbanism, but to find optimal proposals and guidelines, that can be used in the future when forming and selecting the initial concept of planning underground urban spaces, and implementing underground urbanism into the inherited urban norms of the Republic of Serbia. Also, the work can serve as an encouragement to other similar developing countries that strive to institutionalize the planning of UUS in the future.

In ensuring megacities’ sustainable growth, stakeholders are opting for underground space (UUS) utilisation and development. However, further challenges emerge in coastal megacities with soft soil nature and are prone to continuous land subsidence. Thus, future development shall be resiliently planned. This paper presents efforts made towards establishing a model that comprehensively assesses the cause-effect of the uncertain multi-mechanisms revolving around coastal megacities by making attempt to comprehensively assess them via mixed statistical and spatial methods encompassing structural equation modelling (SEM) or regression, spatiotemporal, scenario spatial modelling with the minor comparison between developed and developing megacities. Data collated secondarily from multiple sources. The situation in the COVID-19 pandemic years of 2020–2021 is also analysed. Preliminary findings include (1) the spatiotemporal patterns between Shanghai and Jakarta growing in parallel, (2) the projected spatial growth pattern by 2035 BaU is in line with the 1990–2020 spatiotemporal pattern, (3) Tunnels and UUS construction are surprisingly in continuous manner with stagnant progress of leakage and subsidence during COVID-19 period, and (4) Further research input is proposed to better the model. These attempts of comprehensive monitoring and planning methods by understanding the complex cause-effect relation in large coastal megacities via spatial forecasting and big data can be further replicated and improved with complete experts’ validations and data input to potentially being referred by related stakeholders, e.g. urban planners and civil engineers in both developed and developing megacities.

An integrated development, including underground, above-ground, and elevated deck levels, is underway centered around Shinjuku Station, which is used by multiple railway operators and has the world's largest number of passengers passing through it daily. There is a need to improve the current issues of congestion and lack of pedestrian networks resulting from the complex intersections of railway transfer lines and connections between station to town. In addition, major underground urban facilities (railway lines and public parking lots) need to be updated at the west and southwest exits of Shinjuku Station. By utilizing 3D digital technologies such as BIM models, we are preparing to meet the complex development challenges by creating a database of infrastructure and buildings and examining how to effectively utilize underground space. For the past two years, the Tokyo Metropolitan Government has been experimenting with the latest technologies, such as autonomous driving, in the area west of the station, and it is expected that the development of the station will proceed in a manner that integrates such technologies. Nikken Sekkei leads the overall development of the complex intertwining of various elements, including Shinjuku Station and the surrounding urban area.

Recent research projects have targeted the hitherto limited inclusion of the subsurface and its geo-resources in spatial planning in Sweden. The UNDER project focuses on the societal implications of using the concept of geosystem services to support planning practices. The concept of geosystem services has been described as the contributions to human well-being from the abiotic world or from the subsurface, and although not yet fully defined, the concept has the potential to communicate the many services provided by the subsurface. The project is a case study-driven project and works in collaboration with Swedish municipalities to understand how governance structures support the identification and assessment of geosystem services. Four ongoing spatial planning processes in Swedish municipalities have been selected as case studies, which will provide a variety of spatial planning contexts and objectives. This paper will discuss our methodology and engagement with the different cases. The cases will help us investigate how the concept of geosystem services supports planning processes by mapping these services, exploring how different geosystem services are valued and to develop tools for identification and evaluation. The outcome of the project will provide a robust foundation for advancing spatial planning processes, with the inclusion of geosystem services.

With the rapid development of urban metro networks, the transit-oriented development (TOD) of the metro station has become more and more popular. With the high-intensity development of the upper spaces, the underground public spaces of the station area, including underground pedestrian, commercial, and service spaces, play an important role in connecting the station and the surrounding development plots and the links among the development plots. If the space extension development scope is too limited, the site benefits of the metro station will not be fully realized. Otherwise, if the extended development scope is too amplified, some spaces will be idled and wasted. Especially in the densely developed area of the metro station area, once the underground space is completed, it will be difficult to change. Therefore, the planning of underground public space in the station area is very important. Facing this reality, the study takes the Xietaizi metro station in Chongqing City as an example. Based on the station scheme and the current situation of the station area, the BIM basic model of the underground public space in the station area is constructed. Its synergy with the natural geological conditions, construction conditions, environmental resources, and other aspects are inspected. On this basis, GIS technology is applied to study the accessibility of the underground public space and other traffic conditions in the station area. Integrating various other factors, the potential of space development is studied and the BIM basic model is adjusted and optimized. Through multiple rounds of analysis, the method will serve to formulate the scientific plan of the underground public space, and even the overall space of the metro station area.

Urban underground space (UUS, i.e., built environment) is considered a valuable and non-renewable resource, and considerable research has been devoted to attaining sustainable UUS use. However, UUS use remains mostly characterized by an ad-hoc, first come, first served, or last resort practice which leads to unsustainable development of the urban underground. As more cities realize the importance of the subsurface, there is a growing need for a structured framework for upscaling sustainable UUS practices and transitioning toward a sustainable use of the subsurface. This article investigates how transition management (TM) as a governance theory and operational policy model, aimed at dealing with long-term desired change and sustainable development, can guide the necessary change toward sustainable UUS use. The research connects two streams that have not been closely aligned in the past and focuses on the question: How can transition management help in making sustainable UUS use more common practice? By applying TM key characteristics and instruments to the dysfunctional system of UUS space we demonstrate feasible pathways to upscale sustainable UUS practices.

The World Bank has reported that urban areas currently accommodate over 50% of the global population, with this figure set to increase significantly over the coming decades. To cater to this influx of inhabitants, underground infrastructures must be developed within cities, creating additional space for individuals to thrive within urban environments. Concurrently, there is a growing interest in the colonization of extraterrestrial lands, made possible through advancements in space technology and exploration. In both cases, the habitable regions are confined within inhospitable environments, resulting in similarities in typical habitation structures. However, underground cities have the advantage of egress being possible within a few minutes, while the challenges of space colonization include radiation exposure, extreme temperatures, a hard vacuum environment, and a return trip to Earth of approximately a week. This paper seeks to examine the urban components, city image elements, and challenges of underground city spaces, intending to develop a framework for the urban characteristics of extraterrestrial colonies. The goal is to gain an understanding of the urban characteristics of underground cities and space architecture to develop guidelines for city development in challenging environments.

Cavern development in Hong Kong is entering a new era, from a narrow range of uses in the past to the recent widespread applications in the territory. Rock caverns are now engineered to become a viable source of land supply for sustainable development in Hong Kong. The Government of the Hong Kong Special Administrative Region (HKSAR) has launched a territory-wide Cavern Master Plan, expanded the list of land uses suitable for cavern development in the planning guidelines, selected a group of municipal facilities for relocation to caverns, and implemented other enabling measures with a view to unleashing the full potential of the sustainable multi-dimensional land development approach. In recent years, with the aid of these initiatives, the use of caverns is no longer limited to the “not-in-my-backyard” (NIMBY) facilities but expands to a broader spectrum of land uses. This paper gives an overview of the holistic strategy to direct a new future of cavern development in Hong Kong and provides an update on the progress of various initiatives, including two new caverns projects in the pipeline, viz. the relocation of the Public Works Central Laboratory and the development of the Government Records Service’s Archives Centre. To enable the projects to be delivered in a cost-effective manner within a tight schedule, many novel ideas have been adopted in the planning of these new facilities, including adoption of innovative construction and procurement methods to fast-track the programme. Application of new advanced technologies such as vibration resistance sprayed concrete lining and digital rock mass characterization will also be discussed.

The construction of underground parking system has been widely used in the central business districts of major cities in China, but the arrangement of entrance and exit spacing of underground parking units is unreasonable. This leads to low operation efficiency and a low utilization rate of the underground parking system. However, whether the distance between the entrances and exits of underground parking units is reasonable depends on whether the upstream and downstream functional areas of the entrances and exits of underground parking units will overlap. Overlapping functional areas will cause queuing congestion between entrances and exits when vehicles enter or exit the underground parking unit. Through the analysis of factors affecting the distance between the entrances and exits of the internal parking units of the underground parking system, the calculation model of the elements of the upstream and downstream functional areas of the entrances and exits is proposed. The research results provide a reference basis for the reasonable layout of the internal parking units in urban underground parking system and have a certain guiding significance for planning and design of underground parking system.

From a worldwide perspective, China is the country with the fastest development and the most planning practices for urban underground space (UUS). Looking back over the past 40 years, the practices of UUS planning have gone through four development stages, firstly the exploratory stage of civil air defense engineering combining peacetime and wartime, secondly the rising stage led by a few pilot cities, thirdly the prosperous stage of standardized guidance and national promotion, and fourthly the innovative stage of coordination between ground and underground, and gradually forming UUS planning system with distinctive Chinese characteristics. This article analyzes the main characteristics and representative practical cases of the four stages, and deeply analyzes the problems and reasons that exist in current practice from five aspects: the differences in UUS planning between China and foreign countries, the necessity of UUS planning, reconstruction of UUS planning system, upgrading of UUS planning methods, and improving the efficiency of UUS planning implementation. Then it proposes targeted main ideas and suggestions. The future city will be a three-dimensional city with integrated development of ground and underground. China’s practical exploration will contribute more wisdom to the development and utilization of UUS in Global city.

Hong Kong (HK), one of the most densely populated cities in the world, is characterized by a rugged hilly topography that covers about 60% of the land area. Nonetheless, this natural condition provides a good potential for rock cavern development as an alternative source of land supply. To unleash the potential of these ‘hidden’ land resources, a territory-wide Cavern Master Plan with an Explanatory Statement and Information Note was published by the HKSAR Government in 2017 as a planning tool to guide and facilitate the wider application of cavern development in HK. To prepare for the future development of HK, with technological improvement, the cavern development protocol has been evolved and enhanced. This paper discusses the enhancement of rock cavern development including the planning strategy as well as the engineering solutions to create synergy through better integrating cavern development with the surface and subsurface developments as well as the wider district and territorial planning strategy to ensure optimal use of land resources.

Metro-led underground space (MUS) plays a crucial role in urban underground utilization. Extensive engineering cases have shown that optimizing the disaster resistance ability of MUS has practical significance. However, current research mostly focused on qualitative exploration from the perspective of structural disaster prevention, which proposed the strategies typically targeting the interior of single buildings, lacking coupling to the surrounding space. In order to fill the gap, this study models the MUS into a topological network, measures the robustness of MUS, formulates a MUS robustness evaluation model, and selects two disturbance modes namely random attack and deliberate attack. Then this study sets People's Square Station and Wujiaochang Station in Shanghai, China as cases, computes the classic indexes, analyzes the performance of each case, and summarizes the layout indications.

Increasing use of the internet, cloud services, and online storage of vast amounts of data and information have amplified the need for data centres across the world. These centres are energy-intensive and require cooling around the clock. With the case example of Helsinki, Finland, the paper highlights the value of embedding principles of circularity and resource efficiency in the design, construction, operation, and maintenance of underground data centres to reduce emissions, consumption of resources, and costs of energy.

Urban resilience is the ability of an urban environment, including its infrastructure and inhabitants, to remain functioning in the face of acute shocks and chronic stresses. This paper explores the role underground space plays in urban resilience, considering both short-term events and long-term changes. Underground structures are inherently resilient against damage caused by natural disasters, such as earthquakes, but they can be at higher risk of damage due to sudden flooding. The risk of flooding requires special attention in the context of climate change, as the risk of sudden flood events rises. At the same time, underground space offers opportunities to help reduce climate change impacts, and use of underground space is essential in realizing compact and energy-efficient cities, and as such is an essential component of a resilient city.

Underground work spaces (UWS) are a potential alternative to traditional aboveground office buildings. In addition to potential benefits for tenants, such as being more energy efficient and controllable, UWS may also contribute to a country’s resilience by providing shelter from disasters. This study analyses UWS through the Strength, Weaknesses, Opportunities, and Threats (SWOT) framework. Primary data were collected through questionnaires and interviews with workers in UWS and professionals in fields related to UWS. Secondary data were collected from a review of published literature. The SWOT analysis was conducted by identifying both internal and external factors that may affect UWS, analysing their potential impact, and developing an action plan to improve the acceptance of UWS and mitigate negative impacts. The SWOT analysis reveals that the strengths of UWS include more efficient land use, unique design, and a sense of community. However, UWS often suffer from a lack of natural light and external views through a lack of windows. These could affect employee productivity and morale. Opportunities for UWS include new uses for existing space, the ability to design for connectivity, and protection from climate change. Perceptions of potential users and the general public were highlighted as the biggest threat to the adoption of UWS, alongside technical difficulties in maintenance resulting in poor environmental quality. Our SWOT analysis provides valuable insights for both academics and industry. While UWS have some limitations and potential drawbacks, there are also clear advantages and ways to mitigate limitations and even turn them into strengths. As the most visible threats to UWS adoption relate to potential workers and occupiers, more effort should be concentrated on presenting the benefits of UWS to the public and identifying ways to improve the UWS experience to change worker perceptions. The findings from this study can inform future decisions regarding the viability of UWS.

Given the lack of consideration for the safety of the surrounding environment in existing layout planning research for newly constructed Urban Underground Space (UUS), this study proposes a novel resilience evaluation model for UUS development through the cross-application of geotechnical analysis, urban planning theory, and artificial intelligence (AI). By re-using geological information, the proposed model mapping algorithm enables the application of geological models to refined numerical calculations, accurately locating the range of excavation disturbances of new UUS. Subsequently, the proposed AI algorithm is trained to learn from the existing underground space excavation cases, establishing a mathematical mapping relationship between the main construction parameters and the safety indexes of surrounding buildings. The mapping relationship enables the assessment of the development resilience of UUS through the safety evaluation of surrounding affected buildings and forms an intelligent resilience evaluation model of UUS development. This study contributes to the tools and methods for UUS layout planning and seeks the breakthrough for the cross-application of geotechnical science and urban planning theory.

Enhancing the disaster prevention capacity of cities has emerged as a significant concern in current urban development. Given the growing emphasis on Urban Underground Space (UUS) development, it holds immense importance to accurately assess the disaster resilience of Urban Underground Infrastructure (UUI) and its development trend for a comprehensive understanding of urban disaster prevention capabilities. This research paper introduces the concept of disaster persistence to elucidate the ability of facilities to sustain their operational functionality amidst disruptive disasters. Based on disaster theory, the factors influencing UUI disaster persistence to three critical disasters, namely earthquakes, fires, and urban flooding, are identified. Accounting for the interplay among these factors, an Analytic Network Process (ANP) network structure model of influencing factors is formulated. From the perspective of time evolution, considering the construction condition of facilities, surrounding natural conditions, and governmental management, a regional UUI disaster resilience evaluation framework is proposed to reflect dynamic changes over time. It is anticipated that this study will enhance public comprehension of the disaster prevention value associated with UUS, while concurrently offering technical support for future urban planning and design endeavors.

The use of the urban underground space has been regarded as a major contributor to urban environmental sustainability because it has consistently offered efficient solutions to the growing problems that modern cities face. Recently, underground development in urban areas has attracted more attention due to the increased pace of urbanization and the negative consequences associated with it. The range of underground space uses is constantly expanding as city authorities acknowledge the important role of underground development in their efforts to meet the sustainable development goals as well as improve the resilience of contemporary urban areas. On these grounds, underground farming has emerged as a new and quickly developing use of the urban underground space. Currently, examples of underground farming can be found mainly in developed countries aimed at ending hunger and achieving food security, owing to the safety and security features of the underground space against climate change and natural or man-made disasters. The focus of this paper is on microgreens. Using the urban area of Athens, Greece as a reference, the paper analyzes the design concept of an underground microgreen farm utilizing modern hydroponics. The underground farm is examined by means of a feasibility study. The results show that underground microgreen farming can be a profitable business opportunity, while at the same time improving food security for people living in overpopulated urban areas. Furthermore, underground microgreen farming provides additional benefits in terms of resource and energy efficiency and minimization of transport costs.

The lack of space above the ground has forced human civilization to go underground for sustainability. It is not only space but also comfort that plays a key role in the development of such an underground structure. Nevertheless, it is crucial to acknowledge that underground structures, specifically tunnels, are vulnerable to fire and blast loads in the event of terrorist attacks. This rise in temperature due to fire, when accompanied by external threats like bomb blasts or missile attacks, may adversely increase the geothermal gradient at the point of action. Hence, necessary numerical studies need to be carried out to assess the effect of these kinds of external hazards on underground structures. In the present study, a combined fire and blast analysis of a tunnel built in sandstone rock is performed to predict the geothermal gradient generated across the tunnel cross-section. A three-dimensional non-linear finite element numerical model was developed with a circular tunnel of diameter of 5.6 m and in a rock domain of 200 m × 200 m × 200 m using ABAQUS GUI Interface. Initially, the thermal analysis was carried out with application of heat flux time history at the center of tunnel. Thereafter, the blast analysis was carried out for 50 kg PETN explosive at the center of the tunnel. The study conducted herein shows the strength degradation due to the thermal effect in the tunnel periphery. The findings of the study indicate that the critical zones susceptible to damage are primarily influenced by the magnitude of the pressure. This information can create an insight into the design of resilient underground structures with improved safety.

This paper addresses the urgent need for a comprehensive carbon assessment framework in tunnelling construction to achieve Net Zero Carbon by 2050. Current practices lack granularity and specificity, particularly for Tunnel Boring Machine (TBM) tunnelling, which hinders the identification of early carbon reduction potentials. To overcome these issues, this paper proposes applying the EN 15978 system boundary to tunnelling projects. This innovative framework emphasizes the importance of early design decisions, particularly in the selection of materials and specifications for segmental linings and the performance modelling of TBMs. The proposed method, validated through case studies, paves the way for better estimation and reduction of greenhouse gas emissions in TBM tunnelling. This holistic approach contributes to the broader goal of decarbonization in the construction sector, supporting global efforts towards sustainable development.

The complex geological environment, hydrologic environment, and the vulnerability of tunnel structure bring high risk to the structural safety of submarine tunnel. To scientifically evaluate the resilience of undersea shield tunnels, this paper proposes a resilience evaluation system for tunnel engineering in complex environments based on a knowledge graph. The proposed approach analyzes the resilience characteristics of material properties and structural modes, adopts system resilience enhancement theory, and coordinates disaster prevention during both construction and operation periods. Resilience evaluation standards are established and tunnel deformation is monitored in real time. The above information about resilience is collected and sorted to form a data layer. A knowledge graph is constructed based on the data layer to evaluate the resilience of the tunnel structure automatically. The Qingdao Jiaozhou Bay Second Undersea Tunnel Project is used as a case study for engineering resilience evaluation and enhancement, providing a reference for the application of resilience theory in tunnel engineering.

Utilisation of the underground has not reached yet its peak in diversity and complexity, but in general been attractive for developers of road-, railway- and metro projects. Understanding of rock mechanics, engineering geology and geology can be utilised to give underground applications a wider perspective than until now. This paper focuses on challenges ahead; where does the tunnelling industry go with respect to utilising the underground?The easy tunnelling and underground projects are done, the industry faces projects in the future that request high confidence and understanding of the properties and capacities held by the rock mass. These capacities need to be engaged to solve the requirements to future underground applications.There is a shortage of energy worldwide. Future energy development has to include underground facility to a much larger extent than today.This paper will touch base on the utilisation of future applications of the underground use and discuss certain and a selected number of utilisations, this may not necessarily be limited to energy development but could also be other kinds of utilisations that can be considered somehow out of the box. The main message is: In the future development of our societies, the use of the underground will see a much wider variety of applications, and thus the tunnelling industry must prepare for this development. What is known already is that; utilising the underground provides a solution that; is safe from external load and sabotage, is safe from earthquakes, is safe from climate change impacts like flooding and wood fires, is safe from natural catastrophes like tsunami. But these solutions may come with a high cost ratio which the industry needs to deal with and there is an uncertainty related to public consensus. In addition, the future will request even higher concerns on reduced emissions and increased focus on sustainability. The paper consists of my personal views after almost 40 years in the tunnelling industry. All views presented herein are based on this experience base and represent the way I foresee that the tunnelling industry and competence within this industry can contribute to reach the UN global sustainability goals, to reach the desperate battle against global warming and not least to reduce the consequences on third parties resulting from dissension that the global community faces from time to time, nowadays the conflict in Ukraine. Going underground provides solutions for social security, urbanisation and emission reduction and realise satisfaction of many UN-sustainability goals.

Gas explosion is one of the potential disasters in utility tunnels (UT) that may pose a great threat to the structures and surrounding environment because it features high frequency, short duration and high overpressure. Structural response and vulnerability analysis of UT under gas explosion load are different from the existing seismic vulnerability analysis theory. In this study, dynamic response of UT is analyzed with a set of numerical models based on the coupling of arbitrary-Lagrangian–Eulerian (ALE) and finite element (FE) algorithms by observing overpressure, displacement and effective stress. By combining characteristics of gas explosion loads and dynamic response of UT, this paper proposed the method of structural vulnerability of UT under gas explosion load, which can provide a theoretical basis for risk analysis of gas explosion and the resilience design of UT.

With the onset of the twenty-first century, an increasing number of tunnel projects have been initiated in intricate and challenging environments. Traditional risk assessment methods have struggled to harness the wealth of monitoring data effectively and provide precise guidance to personnel in the event of risk incidents. To tackle these issues, this paper takes the risk of water inrush as an illustrative case and employs knowledge graph technology to establish a comprehensive water inrush graph database encompassing monitoring data, risk mechanisms, and mitigation guidelines. This initiative enhances data utilization and augments the risk management capabilities in tunnel engineering.

It is known that antifreezing agents scattered around the entrance of a road tunnel are transported into the tunnel by running vehicles. Most of the antifreezing agents are mainly composed of chlorides, and their adhesion to appendages in tunnels is one of the main factors that promote corrosion deterioration of appendages. Therefore, it is necessary to grasp and evaluate the effect of scattering antifreezing agents on the amount and location of adhered salt in road tunnels. However, the effect has been hardly grasped and evaluated at present. In this paper, multiple stainless steel plates were installed at the entrance part of road tunnels, and the adhered salt was collected and analyzed from the surface of plates after the exposure period. As a result, it was clear that the scattering antifreezing agents and running vehicles may promote the corrosion deterioration of appendages in tunnels depending on the position in a tunnel.

Fire safety is an increasingly important topic in the underground space. This study aims to contribute to this growing area of research by establishing a holistic framework for shield tunnels and provides new insights into the performance-based analysis. Results from experimental studies on the fire performance of the shield tunnel are presented under the combined effect of fire and structural loading. Test variables included fire exposure, load level, restraint conditions, etc. The experimental investigation has shown the basic failure mechanism of shield tunnel structure in fire. Data generated from fire tests is used to validate models developed for evaluating the fire response of the shield tunnel under any specified fire, loading, and restraint conditions. The multi-scale thermo-mechanical models accounts for critical factors governing structural fire response with fire exposure duration. Results from validation show that the models can capture the fire response of the shield tunnel structure with reasonable accuracy in both thermal and structural domains. Numerical analysis from single ring to multiple rings reveals that the entire structural failure occurs due to localized elevated temperatures. As far as the models concern, an alternative design methodology is introduced based on the concept of maximum allowable deformation, which is exemplified in multiple case studies. The methodology proposed aims at shield tunnels upon the knowledge of fire safety engineering to obtain more trustworthy performance-based designs, and therefore demonstrates adequate fire safety performance. This new understanding should help to improve predictions of the impact of the fire on the shield tunnel and have significant implications for design and maintenance.

Traditional deterministic analyses of tunnel face stability often neglect the uncertainties of geotechnical parameters, while simplified reliability analyses fail to account for soil spatial variability. To overcome these limitations, this study proposes an efficient framework for the reliability analysis and design of tunnel face stability. A probabilistic framework is proposed by coupling the stochastic limit analysis model with the improved Hasofer-Lind-Rackwits-Fiessler recursive algorithm (iHLRF)/inverse iHLRF algorithm. The proposed method allows for rapid and precise reliability analysis and design of tunnel face stability while considering soil spatial variability. An example of tunneling in frictional soils is used to demonstrate the feasibility and efficacy of the proposed method. The results show that the proposed method successfully assesses the reliability of tunnel face stability and carries out a reliability-based design (RBD) of support pressure in the presence of soil spatial variability. The results also demonstrate the feasibility of using the forward and/or inverse first-order reliability method (FORM) in high-dimensional problems.

Risk management is crucial in ensuring the safety and efficiency of Tunnel Boring Machine (TBM) excavation by preventing adverse accidents. Unfavorable geology is a significant source contributing to such accidents, increasing the probability of their occurrence. However, conventional approaches have limitations in adequately addressing the complex and uncertain nature of accidents that occur during TBM tunnelling. This study proposes a probabilistic-based TBM risk management model based on Bayes’ theorem. The model utilizes case studies of TBM accidents to explore causal relationships within intricate and uncertain problems. The initial step involved establishing a TBM risk database through case studies of TBM accidents. Statistical analysis of the database enabled the computation of two types of probabilities: P(Source∣Accident) and P(Source∣AccidentC), for each causal combination. Subsequently, the posterior probability, P(Accident∣Source), was calculated using Bayes’ theorem. The risk level was determined based on the change ratio of the posterior probability compared to the prior probability, P(Accident∣Source)/P(Accident). The results of the study identified the fault zone and weak ground as the critical causes of face collapse. Furthermore, three out of five causal combinations related to excessive deformation were classified as having an intolerable risk level. Interestingly, none of the identified sources were associated with water/mud inflow accidents. In conclusion, the proposed model can serve as a valuable guideline for risk management in TBM construction, enhancing both safety and efficiency.

In recent years, the construction of branched tunnels has increased in cities to facilitate the interconnection of urban transportation systems. However, these bifurcated sections create a complex traffic flow state, thus posing a higher fire risk. Moreover, the rapidly changing boundaries at the tunnel traffic merging section will cause a complex fire and smoke transportation behavior once a fire occurs. Previous studies have observed the lateral deflection of flames towards the sidewall under natural ventilation conditions, whereas the effect of ventilation conditions and associated temperature distribution characteristics are still unknown. In this study, the effect of inflow conditions and heat release rate (HRR) on flame behavior and temperature distribution in the tunnel traffic merging section was studied with a set of reduce-scale model experiments. Results indicate that the temperature distribution at the traffic merging section shows a strong multidimensional feature due to the coupling effect of rapidly changing boundaries and the fire buoyant-induced flow. As a result of multidimensional flame deflection, the location of the maximum temperature on the ceiling deviates from the center axis. Finally, a prediction equation to evaluate the maximum ceiling temperature is proposed by introducing confluence velocity to modify the classical plume theory. This work contributes to a more comprehensive understanding of the fire dynamic theory in bifurcated tunnels and can inform the development of effective fire safety measures.

The article proposes a method for constructing multi-hazard action scenarios in the entire lifespan of metro shield tunnels, based on extensive research on hazard cases and defect data. This method involves combining the tunnel’s health state field with sudden hazard scenarios, and it identifies various multi-hazard scenarios that should be considered throughout the tunnel’s lifespan. Subsequently, a simplified multi-hazard scenario is employed to analyze the tunnel’s structural response. The computational findings reveal that accounting for tunnel defects results in greater structural damage. Moreover, the structural damage is significantly amplified when multiple hazards effects are taken into account, thus underscoring the importance of considering multi-hazard scenarios in the analysis of structural damage.

The increasing exploitation of underground space has resulted in numerous oversized excavation projects which entail widely distributed risk factors and therefore demand a real-time risk management without blind spots. To facilitate vision-based risk identification and management, this study develops a comprehensive image dataset labeled in semantic mask level and an enhanced semantic segmentation algorithm to enable visual detection of the precise boundaries of construction objects on oversized excavation sites. Taking an oversized deep excavation project in Ningbo, Zhejiang Province, China as the case study, we first created an image dataset comprising real images, synthetic images generated from BIM, and web images crawled from the Internet. Ten classes of objects in construction activities of excavation sites, including worker, machine, and structure were selected as the target objects and finely annotated. A DeepLabv3+ algorithm modified with a lightweight MobileNetV2 backbone network and sub-pixel convolution (MobileNetV2-s) was employed on the developed dataset. Moreover, a compound loss function and transfer learning technique were leveraged for better algorithm training. Results demonstrate that MobileNetV2 achieves a mIoU of 69.67% and a mPA of 83.81% with an inference speed of 37.17 frames per second at a resolution of 1280 × 720 pixels, which strikes an optimal balance between performance and efficiency. The present study offers a promising solution for more efficient and reliable vision-based risk identification and management in oversized excavation projects.

Urban underground space development is widely accepted as a contribution to urban resilience. An in-depth understanding of the composition and influencing factors of this contribution can help to better exploit the resilience of urban underground space. Currently, research on underground space resilience is mostly at the macro level (city scale) but lacks micro level (district scale) exploration. To bridge this gap, this study constructs an evaluation framework to measure the contribution of underground space in key urban areas to urban resilience enhancement. Under this framework, the evaluation index system is established from a systematic perspective and the relative importance of indexes is estimated by entropy weight method. The framework is then applied to evaluate representative cases in Shanghai, i.e., cases in sub-centers characterized with a multitude of metro-led underground space and underground complexes. The results show that underground space has multi-dimensional contributions to urban resilience at the micro level, with providing reachability to exits, protection space enhancement, and environmental benefit enhancement being the top three positive contributors, while underground space vulnerability is a non-negligible negative factor. The findings can provide guidance on urban underground space development toward a more resilient direction.

The uneven deformation of urban strata is difficult to be detected at the early stage of development due to the influence of ground improvement, while the buried pipelines can more conveniently sense this uneven deformation. In order to study the relationship between the deformation of a buried pipeline and the specific distribution of the strata deformation, a model test box with controllable shear value was built for this paper, and the deformation state of the pipeline was obtained by monitoring the strain and displacement during shear. The results show that the shear force and shear displacement of sand under the external shear force were roughly linear related, but its shear strength would rapidly decrease when the slip zone was penetrated, and the shear slip zone of sand had an olive-shaped curve distribution. The buried pipeline produced an S-shaped bending deformation along the longitudinal direction under the action of ground shear, and eventually, the bending failure points will appear on both sides of the shear slip zone.

Tunnel lighting is important for driving safety in tunnels. Currently, the emphasis on the study of tunnel lighting has expanded from safety to energy saving and visual comfort. This paper makes a bibliometric analysis of relevant literature using CiteSpace, and summarizes the current research trends and future development directions. Firstly, a keyword timeline graph was drawn by CiteSpace to provide a visual representation of the literature in the field of tunnel lighting. Then the literature is reviewed in terms of two aspects: energy saving and visual comfort. Current research mainly focuses on lamps, auxiliary lighting and lighting systems to save energy. With the development of technology, intelligent tunnel lighting control systems can incorporate more control factors and target parameters to further meet the requirement of saving energy. It focuses on the effect of physical quantities (luminance, color temperature, color rendering, etc.) on drivers’ visual comfort. However, there is still room for tunnel lighting to develop in achieving the unity of energy saving and visual comfort.

This paper deals with the modelling of a longitudinal ventilation system of a road tunnel and the simulation of different fire scenarios. Initially, the analysis of the current traffic and environmental conditions is carried out, in order to model the tunnel ventilation system. Afterwards, different fire simulations scenarios are performed using the Camatt 2.2 (1D) software. The models are developed for different scenarios in terms of the heat release rate and the location of the fire and focus on monitoring the required time for the reduction of backlayering length in combination with the critical velocity and the tunnel’s environmental conditions at the time of the fire. Through these models, the evaluation of the environmental quality and flow characteristics in case of fire event can be drawn, allowing engineers and project safety managers in general to further optimize the ventilation system and to create a healthy and risk-free environment during the operation of the road tunnel.

Tunnel safety equipment is critical for ensuring the safety of road and rail tunnel users in the event of an emergency. However, the required structure, installation, and operation of such equipment can have significant impacts on capital costs, maintenance costs, energy consumption and related CO2 emissions. This paper explores the key sustainability aspects that must be considered when planning and operating tunnel safety equipment in road and rail tunnels. These aspects include minimizing energy consumption, reducing greenhouse gas emissions, minimizing waste generation, optimizing land use, improving accessibility, enhancing safety and security, and ensuring social equity. The paper also examines various case studies of sustainable tunnel safety equipment from around the world, highlighting best practices and lessons learned. The findings of this paper demonstrate that sustainable tunnel safety equipment is not only necessary for addressing environmental concerns, but it can also provide economic benefits such as reduced footprint, lower operating costs, and increased safety for tunnel users.

Over the past few years, heavy rainfall events exhibited an increasing trend worldwide, frequently resulting in flooding of subway stations. This is particularly concerning in China whose urban underground space is undergoing a rapid development. Once floodwater enters a subway station, it becomes rather difficult for passengers to find escape routes, as water flow can impede the crowd’s movement and damage power systems, ultimately hampering emergency response efforts. Based on these considerations, a series of numerical simulations were conducted to explore the flow patterns when floodwater flowed downwards along the staircase of the subway station. In this study, human legs were simplified as cylinders on staircase steps to capture the fluid-human interaction. Then, the effect of various locations of cylinders on human instability was investigated via multiple staircase models. The results indicated that the greatest moment to which human legs were subjected occurred on the downstream step, while the largest drag force appeared on the rest platform. The findings yielded from this study will be helpful references for designers and engineers to determine hazard mitigation and evacuation measures in case of subway station flooding.

The development of a system to monitor the tunnel face is an urgent issue because of the problem of occupational accidents caused by “rock fall,” i.e., the collapse of rock and sand near the tunnel face immediately after excavation. In this study, we aim to prevent damage caused by rock fall by acquiring information on the tunnel face using various sensors and evaluating the risk of rock fall based on this information. We focused on the overhang of the rock and tried to identify the overhang area using photogrammetry and a 3D sensor equipped with LiDAR.

Makeup air plays an important role in smoke control of building fire. Based on the evacuation behaviour of people in fire environments, makeup air was only supplied in the evacuation passageway in this study. Effects of breathing zone lateral makeup air supplementation and underfloor makeup air supplementation on fire smoke control in subway tunnel were discussed, respectively. It was found that breathing zone lateral makeup air supplementation could prevent part of the smoke from spreading to the evacuation passageway. Due to entrainment, makeup air was mixed with smoke, resulting in the CO concentration that did not meet the relevant evacuation requirements. In addition, breathing zone lateral makeup air supplementation had significant disturbances on the fire and smoke layer. The underfloor makeup air supplementation had fewer disturbances to the fire and smoke layer. However, neither the temperature nor the CO concentration could meet the evacuation requirements. Therefore, breathing zones combined with underfloor makeup air supplementation were applied in this study. The results showed that the combined makeup air supplementation created a relatively safe evacuation passageway, and the temperature, CO concentration, and visibility in the evacuation passageway could all meet the relevant evacuation requirements. This study is expected to provide a new idea for the design of tunnel fire smoke control system.

In this study, we conducted experiments to reveal the mechanism of natural ventilation in deep-underground spaces. Through the combination of various basic units, we constructed a natural ventilation loop L, and the results proved the feasibility and reliability of natural ventilation in deep-underground spaces. Moreover, we proposed a fire evacuation route in a reverse ventilation airflow direction. By combining basic unit groups to share the air shaft, the natural ventilation provided a reliable channel for fire evacuation.

A reliable and efficient ventilation system is a crucial technical measure to address the pollution of dust and harmful gases during tunnel construction. In many cases, the required airflow for tunnel construction is significantly lower than the designed fan capacity, which leads to high energy consumption and low efficiency. Therefore, it is essential to choose an appropriate fan operating frequency for the ventilation system based on the concentration of pollutants generated by different tunneling processes. In this paper, an intelligent ventilation system with fan frequency regulation is designed based on the embedded system. It can adjust the frequency of the fan according to the tunnel environment. The system has been implemented in a construction tunnel in China for over two months and has demonstrated satisfactory performance in improving the environment. The results of historical data analysis show that the system can reduce electricity consumption by approximately 31% compared with the manual control method.

Heat release rate, HRR, is significance for the design of rescue and evacuation engineering of highway tunnels, which can be estimated by multiplying mass loss rate, $$ \dot m$$ m ˙ , and effective combustion heat, ΔHceff. In previous paper, only the pressure effect on $$\dot m$$ m ˙ and ΔHceff was investigated, and $$\dot m \propto {P^n}$$ m ˙ ∝ P n was summarized. There was no agreement on pressure effect on ΔHceff. Thus, field tests of $$\dot m$$ m ˙ and ΔHceff were conducted at 523, 3160, 3500, 3960 and 4160 m. The test environment and free flame matched those of high-altitude tunnel fire to ensure that the measured data were correct, regardless of whether the tests were performed inside or outside the tunnel. Adopting a small vehicle as an example, the HRRs of highway tunnel fires were numerically predicted based on the field test results. The results revealed the following: (1) Both pressure and temperature are important factors of $$\dot m$$ m ˙ . . (2) Based on a global model and flame temperature correlation, a correction method of $$\dot m$$ m ˙ was established. (3) The equation of $$\dot m$$ m ˙  = 3.226 × 10−3 T∞ + 1.621 × 10−3P1.0959 − 1.186 × 10−3 T∞P1.0959 − 0.03127 was obtained, which can predict $$\dot m$$ m ˙ under different pressures and temperatures. (4) A prediction model of ΔHceff = 0.5548P-16.9580 was established based on field test data. (5) The peak HRR of highway tunnel fires at 523, 3160, 3500, 3960 and 4160 m ranged from 3.56 ~ 5.55, 1.20 ~ 2.33, 0.47 ~ 1.54, 0.33 ~ 1.20 and 0.21 ~ 0.90 MW, respectively. The results in this work could provide a basis for other HRR prediction and smoke diffusion studies of high-altitude highway tunnels.

The Government of the Hong Kong Special Administrative Region (“the Government”) regards rock cavern development as a middle-to-long-term land supply option for alleviating the problem of urban land shortage. Valuable surface land could be reserved for other beneficial uses by accommodating or relocating suitable facilities into caverns. Following the successful examples of caverns project for public utilities like sewage treatment works, the Government aims to extend the use of caverns to house other suitable facilities, such as laboratory, in which the population density and fire risk is notably higher. The Project “Relocation of Public Works Central Laboratory (PWCL) in caverns” (“the Project”) is to relocate the existing PWCL to caverns, and about 250 people will work inside the caverns when the PWCL is in full operation. The reprovisioned PWCL will be the first laboratory to be built in caverns in Hong Kong. Safeguarding human life inside the laboratory against fire hazard is of paramount importance, the associated fire risk has therefore been carefully assessed and mitigated. The key challenge arises from the fact that the prevailing fire safety design codes are mostly tailored for surface buildings, which is not fully applicable to cavern facilities. Due to the unique setting of the caverns, there are genuine difficulties to satisfy the deem-to-comply design requirements as stipulated in the fire safety design codes. On the contrary, some specific fire hazards may attribute to the cavern setting or the usage of the facilities and warrant extra considerations. To ensure the fire safety level of the design would not be inferior to that in surface facilities, comprehensive assessment based on Fire Engineering (FE) approach is conducted covering all fire safety aspects, including means of access, means of escape, fire compartmentation and fire services installation. With FE approach, innovative proposal is devised that improves the fire safety level and enables effective firefighting operation. This unprecedented design provides a cost-effective solution without compromising the fire safety standard. It will become the reference for of the fire safety design of future cavern facilities in Hong Kong.

The dynamic responses of ultra-shallow embedded tunnels, such as ground-penetrating shield tunnels (GPST), differ significantly from conventional shield tunnels. The GPST is partially exposed on the surface and partially buried underground. To investigate their characteristics under dynamic motion, large-scale shaking table tests were performed. The model was designed to emulate both the cross-sectional and longitudinal stiffness of prototype tunnels, as well as the site parameters. Simple harmonics with varying significant frequencies were utilized as earthquake motions to excite the tunnel model in both transverse and longitudinal directions. Key aspects studied include the acceleration response and diameter deformation rate to uncover the dynamic characteristics of GPST. The model tunnel's buried depth ranged from −0.5 D to 0.5 D, with negative burial depth indicating that the tunnel's top is above the ground surface. Results demonstrate a strong correlation between the dynamic response and buried depth. Concerning acceleration response, it was found that the acceleration response increases as the buried depth decreases. Specifically, the tunnel's acceleration at the shallowest depth reached four times the input motion. Additionally, the structure exhibited a “whiplash effect,” causing violent oscillations in the overground structure. Conversely, the diameter deformation response indicated that the diameter deformation response increased as the burial depth increased.

Tunnels have become the preferred solution for the development of underground assets, especially in urban areas. Many cities are established in regions constituted by tropical soils which geotechnical behavior differs, to some extent, to that of temperate regions. This peculiarity of soil behavior affects the estimation of ground movement due to tunnel excavation. This paper presents a sensibility analysis using tornado diagrams to address the uncertainties of geotechnical properties for the assessment of tunneling-induced surface settlement. The analysis was conducted on part of the recent expansion of Line 5 of the São Paulo Metro. Two-dimensional (2D) finite element numerical analyses, based on the Mohr–Coulomb constitutive model, were carried out to reproduce the behavior of the tropical soils due to TBM tunneling. For that, data from a series of laboratory testing were used to characterize the stress–strain behavior of the residual soils. The evaluation of the variability of soil parameters was made by considering probabilistic scenarios based on the lower, mean and upper bound values of the coefficient of variation of input variables. The analysis allowed to identify which soil parameters have significant influence on ground movements considered for this case study. Finally, a comparison from the results of numerical analysis with the settlements measured from field instrumentation is presented showing a good agreement.

Accurate prediction of cavities ahead of a tunnel face is essential for ensuring stable and efficient construction. In this study, a harmony search-based optimization system was developed to estimate cavity characteristics ahead of a tunnel face, such as the distance between the cavity and tunnel face, the radius of cavity, and the electrical resistivity of cavity. The relationship between the cavity characteristics and electrical resistivity was derived to apply as the objective function of inverse analysis. The inverse analysis was conducted using the derived analytical solution corresponding to the electrical resistivity values of the ground formations containing a cavity. A series of laboratory experiments were performed to validate the developed system, and the results showed that the system could accurately estimate the cavity characteristics. In conclusion, the developed system can be a powerful tool for minimizing potential risks by predicting cavity characteristics ahead of a tunnel face.

Massive ground subsidence occurred during the construction of the cross passage of two main railway tunnels through a geologic formation bearing unexpectedly high gas pressure near the Nakdong River in South Korea. This subsidence caused structural damage to shield tunnel segments. To replace the damaged segments with box structures, a broad and deep excavation employing diaphragm walls was carried out, and artificial ground freezing was applied to connect the box structures with the intact tunnels outside the diaphragm walls. In this study, a three-dimensional thermo-mechanically coupled numerical analysis was conducted to assess the impact of artificial ground freezing on deep excavation. In order to reduce computational time, a one-way coupled approach was adopted in the numerical model, where the thermal analysis was initially performed considering the geometry and construction process, followed by mechanical analysis that incorporated changes in the ground properties based on the freezing temperature. The proposed numerical model was validated by comparing the results with the in situ measurements. Furthermore, the behavior of tunnel segments located outside the diaphragm walls was numerically investigated in relation to the freezing and thawing process. During the freezing process, the tunnel segments experienced heaving due to frost expansion of the ground, while they subsided during the thawing process.

Soils adhered to cutting tools or clumped to each other could not only cause a low advance rate in tunneling but some difficulties in spoil discharging. These especially hold true while tunneling in the loess containing primarily silt particles. The above remains to be addressed toward preventing unplanned downtimes and additional project costs. In addition to the mixing and fluidity tests, the AFM (atomic force microscopy) test is applied to explore the inherent mechanism affecting their adhesion properties when sand, kaolinite, and montmorillonite are applied as adhesion reduction materials. The adhesion ratio is in a negative relation with the fluidity. The latter two are not deemed good adhesion reduction materials despite the higher adhesion force of the sand-loess mixture than the kaolinite-loess mixture. The intermolecular force plays a key role in triggering such a phenomenon. The highest adhesion force of 52.5 nN is attained by the montmorillonite-loess mixture due to the development of capillary force.

Large infrastructures such as tunnels usually involve complex, integrated, and multi-risk systems, which requires a thorough project designing, construction monitoring and operation management throughout the lifetime. Building information modelling (BIM) and numerical modelling are both beneficial tools for the optimization and decision-making of engineering projects. However, there lacks a framework to combine these two models and to exchange real-time data between them. In this study, a numerical simulation workflow based on BIM is proposed for tunnels, which is not only able to convert three-dimensional parametric geometry models in BIM projects into numerical models, but also able to define material properties for each part of tunnels automatically according to BIM information. The finite element method (FEM) is adopted for numerical simulations, and the numerical model is constructed by automatically generated commands in commercial finite element software packages. First, a detailed tunnel model integrated with geological information, including geographic data, borehole data, and geological profiles, is developed as a BIM project. Then, considering complex geological conditions such as faults, Python codes are programmed for the pre-treatment of numerical models to reduce repetitive manual operations and to improve the simulation efficiency by extracting multi-scale model data. Finally, a case study of Tunnel Angath in Austria is provided to demonstrate the performance of the proposed framework. The coupled BIM-FEM framework offers a fundamental process for automatic design-to-analysis, and can be used for real-time structural calculation for decision-making.

This paper examines the challenges associated with constructing underground spaces on high-filled foundations, using the case study of the northern expansion project at Urumqi Airport in Xinjiang, China. Given the region's collapsible loess soils with extremely low moisture content, dynamic compaction methods were employed after rigorous indoor and field testing. Layered rolling and dynamic compaction techniques were utilized during high-fill construction. The reliability of the engineering scheme was verified through large-scale testing, including deformation monitoring during and after construction. Moreover, the temporal interplay and mutual impact between high filling and underground structure construction are analyzed, with details provided on mitigation measures. Findings from this project serve as guidelines for designing and building underground spaces on comparable high-fill foundations.

Excavation of the Earth pressure balanced (EPB) shield tunnel boring machine (TBM) relies on the viscoplastic nature of excavated soil to maintain face pressure. Soil conditioning is a method that injects additives, such as foam and polymer, to make the excavated soil viscoplastic. Soil conditioning enhances the properties of excavated soil, reduces TBM torque and cutter wear, and improves excavation efficiency. Therefore, it is essential to evaluate the rheological properties of conditioned soil during the excavation of the EPB shield TBM. This study conducted slump tests and laboratory pressurized vane shear tests to evaluate the rheological properties of conditioned weathered granite soil. The prepared soil specimen was conditioned with foam as an additive. The foam was uniformly applied to the soil through the foam generator to meet the target foam expansion ratio (FER). The tests were conducted by changing the water contents and foam injection ratios (FIRs). The slump value of the conditioned weathered granite soil increased as the water content and FIR increased. However, the vane torque, peak strength, and yield stress decreased as the water content and FIR increased. Furthermore, the study confirmed a correlation between the slump value and yield stress.

In NATM tunnels, the concrete lining serves as a secondary support structure playing subordinate roles. However, when the primary support deteriorates or the ground conditions are poor, the lining may be subjected to unexpected earth pressure. To prevent damage caused by this pressure, it is necessary to identify the loosen load, allowing the lining to perform its mechanical function. In this study, a numerical model was developed to simulate the trapdoor experiment and to propose a method for calculating the relaxed load. The discrete element method (DEM) was adopted in the model to represent the characteristics of the ground surrounding the tunnel. The numerical model simulated a series of experimental trapdoor steps and analyzed the ground loosening load. The contact properties of the soil were calibrated by the analysis of the triaxial compression test, and the reliability of the developed numerical model was ensured by comparing the results with laboratory test results. The model calculated the contact force applied to the trapdoor plate and the settlement of the soil particles. By controlling soil characteristics, ground height, and trapdoor plate width, the developed model can analyze the design of tunnel cross-section size and stability under various ground conditions.

Electrical testing technology is categorized as one of the geophysical testing techniques and enjoys widespread utilization in the evaluation of special soil sites owing to its rapid, non-destructive, and precise characteristics. To elucidate the current application status of electrical testing technology in the evaluation of special soil sites, an extensive review of domestic and foreign literature was conducted, encompassing the evaluation and application methods of the electrical resistivity method in contaminated soil, expansive soil, collapsible loess, soft soil, and frozen soil sites. This article further explores and summarizes the application techniques and future prospects of coupling electrical testing technology with existing in situ testing technology for comprehensive evaluation of special soil sites. The analysis reveals that electrical testing technology exhibits favorable efficacy and significant potential for development in the investigation and evaluation of special soil sites, demonstrating commendable performance in regional delineation and monitoring of physical properties in such sites. Nonetheless, additional research efforts are necessary to enhance the interpretation of electrical parameters and mitigate the influence of soil layer characteristics. Simultaneously, it is imperative to conduct research on the combined testing methodology that integrates electrical testing technology with in situ testing technology to offer guidance for the advancement of investigation and evaluation practices concerning specialized soil sites in China.

In order to realize the complementary resources, a series of large-scale water resource allocation projects have been carried out in China, involving fussy designs of shaft structures under complex stratigraphic conditions. In Pearl River Delta Water Resources Allocation Project, for example, 28 circular shield tunneling shafts are arranged, with depths ranging from 34 to 74 m and diameters ranging from 24 to 39 m. Unlike conventional shield tunneling shafts, mechanical performance for the deep and large-diameter circular shafts presents a significant spatial effect, resulting in fussy structural design and inefficiency. In this paper, deformation measurement data of the shafts are first collected and systematically analyzed. A 3D finite element (FE) model is established to consider spatial effects and non-uniform distribution of the adjacent stratum. Furthermore, we accomplished a series of batch processing tasks, including FE simulations under different conditions and extraction of safety control indicators. As a result, we have established a database composed of geometric dimensions, formation parameters, and deformation control indicators. Finally, using machine-learning methods such as Random Forest (RF) and XGBoost for training, a deformation prediction system for the circular shafts in the Pearl River Delta region is constructed based on intelligent information processing technology. The results are quantitatively consistent with the measurement data and FE simulation value, providing an important basis for shaft positioning and structural optimization at the initial stage of design.

Utility tunnel is important for modern cities to transport water, heat, and gas to city core. Its safety is influenced heavily by stratum conditions, extremely by ground fault in Xi’an featured with loess stratum in geology. In this paper, the stress and deformation of utility tunnel are analyzed under the different intersecting angles between ground fault and utility tunnel by means of numerical method. The results show that vertical, horizontal, and bending deformations occur in utility tunnel with ground fault movement, and the deformations are inversely proportional to intersection angle. The deformations concentrate along utility tunnel on both sides of ground fault with a range of 20 m roughly. The top plate of utility tunnel is subjected to compressive stress; the bottom plate is subjected to tensile stress in the hanging wall of ground fault, reversely in foot wall. The maximum stress in utility tunnel decreases with the increasing of the intersection angle. Disconnecting phenomenon takes place between bottom plate and loess stratum, and the disconnecting area is independent to intersection angle. It is recommended to avoid small-angle intersection in the designing and constructing of utility tunnel in loess stratum.

Based on the traditional structural vulnerability analysis framework, the structural vulnerability analysis method considering the fuzziness of the damage states is further proposed and the overall seismic response calculation model of soil-tunnel-ground buildings is established. The membership functions of triangle and quasi-normal shape are introduced to calculate the membership degree of the maximum inter-story displacement angle under different damage conditions to obtain the fuzzy failure probability under different earthquake intensity levels. The maximum likelihood estimation method is used to fit the calculation results and establish the ground-building vulnerability curve considering the fuzziness of the damage limit. The results are compared with the calculation results of soil-ground buildings. The analysis results show that the seismic vulnerability curve of ground buildings given by the fuzzy evaluation method is generally safer. Considering the fuzziness of the damage limit will increase the dispersion of the seismic vulnerability curve of the structure. Moreover, the selection of membership function type has negligible influence on the results of fuzzy seismic vulnerability analysis. The tunnel has a certain amplification effect on the ground-building damage.

The TBM tunnelling industry has lost the technical reasons why backfill grouts are pumped behind the tunnel lining during TBM advance. Primary objective is the avoidance of ground settlements that can be automatically generated by the creation of the annulus void due to the passage of the TBM in the ground. Secondary objectives, not less important, are the avoidance of segment floating, the prevention of water ingress into the tunnel, and the mild transfer of longitudinal and radial stresses from ground to lining. In most of the cases, conventional two- component grouting methods do not fulfil the above basic requirements, thus jeopardizing the quality of the final tunnel and putting at risk the life of people using the final tunnel on daily basis. All backfill grout objectives are strictly linked to raw material quality, TBM operations and the quality of the final tunnel as a product per se. In this context, the backfill grout durability concept is still, anachronistically speaking, highly dominated by the concrete industry mentality where the unconfined compressive strength (UCS) is measured at 28 days; however, accountability on curing of laboratory samples and detailed procedures of testing, quality control are not yet properly addressed by the industry due to the lack of a proper tailored-made standard to regulate TBM backfill grouts. The Global Warming Potential (GWP), defined as the impact of carbon footprint emissions (CO2 eq.) per cubic metre of grout, considering how long it remains active in the atmosphere, is however still rarely calculated. In an average of 300 GWP/m3, cement as binder of component A and sodium silicate as activator of component B are the major contributors of approx. 60% of the total CO2 eq./m3. This paper illustrates a new two-components backfill grout solution with reduced carbon footprint emissions that hopefully will be accepted by the industry.

Rock drillability is an important factor in mining, construction, and geotechnical engineering, among other industries. The drilling rate index (DRI) is a commonly used drillability evaluation method. Typically, DRI values are determined via laboratory testing using brittleness (S20) and Sievers’ J miniature (SJ) drilling tests. However, specimen preparation for these drilling tests is a laborious and time-consuming process that can make it challenging to determine DRI values. This study attempted to estimate DRI values based on mechanical rock properties. The mechanical rock properties include the uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), and brittleness indices (B1–B5) as a function of UCS and BTS. Datasets were taken from relevant literature. A predictive model was developed using symbolic regression and machine-learning techniques. Symbolic regression uses mathematical functions and operations to determine the most appropriate mathematical equation that best describes the relationship between input variables and the DRI in a dataset. Several machine-learning techniques were used, including random forest, decision tree, k-nearest neighbors, and support vector machine. The results showed that the DRI values of rocks can be estimated in a fast, practical, and feasible manner using a symbolic regression model.

Diaphragm wall is widely used in foundation pit engineering as a kind of retaining structure. However, in the case of deep excavation and large width of the diaphragm wall, it is inevitable that the surrounding soil will be disturbed during the construction process, leading to the deformation or even destruction of adjacent structures. Therefore, it is of great significance to explore the surrounding soil disturbance and the foundation deformation of structures caused by the construction of the diaphragm wall. In this paper, based on the field monitoring data of an excavation in Nanjing, the improved genetic algorithm (IGA) optimized long-term memory neural network (LSTM) is used to predict the deformation of structures caused by the excavation of the diaphragm wall. The neural network model was trained, tested, and verified. The results show that the prediction results of the model are very close to the measured data.

Since the suction bucket foundation has been applied in the offshore wind power project, the structure above the mud line bears the actions of loads caused by various marine environmental factors, such as wind, waves, and currents. Currently, the industry primarily focuses on studying the mechanism and force characteristics of the interaction between the pile and the soil. Few researches regarding the integration of the suction bucket-jacket are present. In the study, the equivalent three-dimensional nonlinear spring stiffness is created by the suction bucket-soil nonlinear response analysis through PLAXIS 3D, then combined with SACS to carry out the integrated response analysis of the suction bucket-jacket foundation. The study investigates the structural force and deformation of the suction bucket with the same steel consumption but different sizes. It also examines the displacement at the top of the jacket and the dynamic characteristics of the entire structure under extreme conditions. We found that within the range of 0.8–1.2 slenderness ratio of the suction bucket, an increase in slenderness ratio would lead to an increase in mud depth, a decrease in the displacement of the structure, and an increase in modal frequency.

Underground structures are required in densely populated urban areas where space is limited. Singapore is a country with sparse land space and has several underground structures such as roads tunnels, rail tunnels (mass rapid transit), and common utility services tunnels. Some of these structures were built more than 40 years ago and are prone to structural damage due to water seepage and material degradation. Defects such as leaks, cracks, and spalling concrete due to corrosion damage were commonly found in these underground structures. In this paper, various aspects affecting the durability of underground structures are presented. A study has been carried out to identify major factors contributing to the underground structure damages and to enhance the durability of these structures, as part of this study, three different surface protection methods, namely, impregnation, hydrophobic impregnation, and coating methods have been explored. This paper summarizes the details of surface protection methods and tests carried out to evaluate the effectiveness of surface protection methods to enhance the durability of underground tunnel structures.

This paper presents a novel method for assessing the seismic active thrust in cohesive soils governed by the nonlinear Mohr–Coulomb strength criterion. To characterize the nonlinearity of shear strength envelope, the available studies either simplify it as a linear relationship or substitute a single tangent line for that. However, considering the distribution characteristics of soil stress and the mapping relationships between the strength envelope and soil failure surface, these approximations are a bit rough. To fill the research gap, a piecewise linear method (PLM) is herein introduced, which correspondingly generates a multi-segment rotational failure mechanism according to the associated flow rule. The mechanism can be determined by 2n + 1 (n = 10 in this work) independent angle variables and a time variable. Furthermore, a modified pseudo-dynamic approach is properly implemented to quantify seismic load. This approach involves using a layer-wise summation method to address the earthquake-induced inertial power. The normalized expression of active thrust associated with various parameters can be derived from the work rate balance equation. Then, a classic genetic algorithm (GA) is applied to optimize this multi-variable function. In terms of accuracy, the active thrust obtained by the proposed method (n = 10) is superior to that obtained by the generalized tangential technique (GTT, n = 1), and the improvement becomes more apparent as the nonlinear parameter increases.

The determination of fracturing pressure and failure mode in cohesive soils is a controversial issue that seems to be no consensus among previous studies. In this paper, a novel data-mining approach based on the XGBoost algorithm for predicting fracturing initiation in cohesive soils was proposed. A machine learning framework, including a regressor and a classifier that both have 14 input features and one output variable, was developed for fracturing pressure prediction and failure mode classification, respectively. The engineering verification indicates that the proposed approach paves a new way to predict fracturing pressure and failure mode in cohesive soils, which could provide some guidelines for engineering application.

The expanding utilization of underground space has led to numerous large-scale excavation sites that conceal widespread potential spatiotemporal risk factors. Given traditional manual inspections’ time-consuming, laborious, and inefficient nature, automated real-time inspection of oversized excavation sites without blind spots is crucial for hazard identification and risk management. This paper proposes a deep learning-based model for the real-time detection of construction objects on oversized excavation sites using UAV-captured videos. Based on an oversized excavation project in Ningbo, Zhejiang Province, China, a high-quality dataset has been created using UAVs to collect multi-directional and multiscale site images under various working conditions. The NWD-IoU weighted loss function was incorporated into the state-of-the-art You Only Look Once version 7 (YOLO_v7) network to make the algorithm more suitable for construction sites. The detection performance showed a bimodal distribution, gradually improving as the IoU ratio (IR) increased. The best results were achieved at an IR value of 0.8, resulting in a 17.2% improvement in mAP@.5 and a 5% improvement in mAP@.5:95. The monitoring speed for a video with a resolution of 1920*1080 pixels is 29.97 frames per second, allowing for a precise examination of fast-moving risk actions. This study also addresses the challenges and recommends of utilizing UAVs in object detection within large excavation sites. It provides a reliable, efficient, and economic vision-based measure for real-time information collection and risk management in large-scale excavation projects.

To improve the rock breaking efficiency of TBMs in hard rock, this research attempts to apply hydraulic fracturing technology to assist rock breaking and conduct numerical simulation of multi-step injection fracturing near the tunnel face to find suitable hydraulic fracturing scheme. The simulation results demonstrate that the initiation and propagation directions of hydraulic fracturing cracks are influenced by two key factors: the distance between the fluid injection hole and the tunnel face, as well as the injection sequence. As the initial fluid injection position becomes far ahead from the tunnel face, the propagation direction of hydraulic fracturing cracks gradually changes from vertical to horizontal. The second injection position in the vertical section should not be too close to the initial injection position to prevent the newly initiated hydraulic fracturing cracks converging with the previous cracks. Regarding the arrangement of injection holes on the cross section, when two or three injection holes undergo synchronous fracturing, there is a notable tendency for the fracturing cracks to propagate obliquely and intersect with each other. This intersection results in the rock mass being segmented into smaller blocks, significantly reducing the required fracturing time. Additionally, this process enhances the fragmentation of the rock mass, leading to more efficient tunnel boring machine (TBM) tunneling operations.

The Laifosi Tunnel is a railway tunnel in operation located in Chongqing China, which has suffered from many defects, such as lining cracks, and water leakage from 2010 to 2020. To reveal the mechanism of tunnel defects, on-site boreholes were drilled from some typical sections of the tunnel and specimens were prepared to test for the surrounding rock. A series of laboratory tests were carried out on the rock specimens. The testing results show that the soften coefficient of mudstone is as low as 0.45, which indicates the strength of mudstone decreases sharply. Meanwhile, the grade of surrounding rock is reclassified based on the testing results and field investigations. Compared with the rock grade during tunnel construction, it is found that the surrounding rock near borehole No. 3 has not deteriorated significantly, which is mainly composed of sandstone. However, the surrounding rock near borehole No. 4 has deteriorated from grade III to grade IV from construction stage to present operation stage, which is mainly composed of mudstone. In the tunnel area with abundant seasonal precipitation, continuous deterioration of mudstone caused by long-term water–rock interaction is one of the dominant factors of the tunnel defects. The present research results introduce a theoretical basis for the subsequent treatment of the tunnel defects. It is suggested to consider the rock deterioration during long-term operation when designing and construction a tunnel in areas with such similar geological conditions. For example, the surrounding rock is mainly mudstone and the area is rich in rainfall.

Rectangular underground tunnels (RUT) subjected to complicated asymmetric loads inevitably suffer from uneven longitudinal settlement and cross-sectional torsion. The conventional models for soil-tunnel interaction only focus on the typical single circular tunnel and ignore the effect of torsional deformation and three-dimensional soil reactions. To mitigate this gap, the paper presents a soil-tunnel interaction model for RUT under longitudinal bending-shear-torsion mode. The RUT is regarded as a Vlasov thin-walled beam on Wrinkle foundation, and the soil-tunnel interaction is established considering the five cross-sectional deformation, including torsion, warping and distortion. Based on the new model, the deformation behaviors of RUT subjected to arbitrary loading can be solved through simple programming. Besides, the proposed method is verified by the FEM program.

In the internal support system of foundation pit engineering, reinforced concrete support is widely used in foundation pit due to high load-bearing capacity, unrestricted arrangement, cast-in-place end nodes, and good integrity. However, the disadvantages of reinforced concrete support in design and construction are also significant, including oversized design sections, long construction periods, strong pollution, high costs, and severe waste. Considering the advantages and disadvantages of concrete supports in foundation pit engineering and combining with the characteristics of deep foundation pits in subway cut-and-cover stations, a new type of prefabricated composite steel tube concrete internal support is designed. From the perspectives of improving the stiffness and strength of the end nodes and achieving fixed connections at the ends, a matching new type of end node is proposed, called the “A fixed end composed of long bolts and mold bag concrete.” By elucidating the design scheme, structural characteristics, and working principles of the fixed end composed of special components such as embedded steel plates, hollow flanges, mold bag concrete, and long bolts, it is demonstrated the fixed end functions as a fixed support in the support system. Through the analysis of the mechanical characteristics, failure modes, and evolution laws of the fixed end, the analytical methods for compressive and flexural load-bearing capacities of the fixed support end are obtained. To verify the constructability and construction effect of the prefabricated internal support system, the field technique test of the prefabricated internal support system was conducted.

This paper focuses on the mechanical properties of segment joints in subway shield tunnels. Firstly, a full-scale test is conducted to obtain the whole damage process and bending mechanical properties of a segment joint. The bearing process of the joint can be divided into four typical mechanical stages: concrete elastic stage, inner arc cracking stage, joint overall damage stage, and joint limit damage stage. The critical loads of the adjacent mechanical stage are defined as the joint characteristic loads. Secondly, a series of three-dimensional numerical models is performed corresponding to the full-scale test considering the concrete properties of elastic–plastic damage ontology. The reasonableness of the numerical simulation is verified by comparing the test and numerical simulation results. Finally, the mechanical properties of the segment joints are analyzed parametrically using numerical simulations in terms of material properties and external loads. Through variable reference analysis, it can be obtained that the actual construction of concrete with C60 grade and bolts with 8.8 grade can give the best effect of economic efficiency and improve the performance of joints, and axial force and bolt pre-stress can offset external loads and improve joint stiffness.

The inherent spatial variability of soil properties is the main sauces of uncertainties in the site investigation, and it is commonly characterized using random field theory. Adjacent excavation has a significant influence on the tunnel, which has been investigated in recently years. However, the existing studies usually assume that soil is deterministic, ignoring the spatial variability of soil parameters. Therefore, the objective of this study is to characterize the effect of excavation on adjacent tunnel in spatially variable soil. The Hardening Soil model with small strain stiffness (HS-Small) is used in this study to present the increased stiffness of soils at small strains, a popular choice in excavation engineering. The modulus parameters in the HSS model are modeled as random field. The established numerical model is firstly verified using an actual engineering. There are six indexes to evaluate the influence of excavation on tunnel, including the deformation and angle of tunnel. Meanwhile, an amplification factor simplified method is proposed to present the effect of soil spatial variability. The influence of different relative positions of the existing tunnel and adjacent excavation in spatially variable soil are comprehensively studied. The isocontour distribution diagram of the overall horizontal and vertical movement of the tunnel is given to provide certain references for subsequent similar working conditions.

Bored piles are a popular foundation solution in urban areas where minimal vibration is a prerequisite during construction. Traditionally, bentonite slurry is used to keep a hole open during pile construction. More recently, a synthetic polymer is gradually gaining popularity to replace bentonite support fluid. Compared to the bentonite, polymer fluids can offer a smaller site footprint, ease of mixing, and lower fluid disposal cost. Although some of the field trials suggest that the polymer piles could outperform the bentonite pile under the maximum proof load, to date, no large-scale controlled tests have been conducted which provide an in-depth comparison between piles constructed using polymer or bentonite slurry. This paper describes a set-up of well-controlled large-scale tests on 300 mm diameter, 4.5 m long bored piles, instrumented with strain gauges and distributed fibre optic sensors (DFOS), and constructed in compacted sand at the National Buried Infrastructure Facility (NBIF) using both polymer and bentonite slurry as the supporting fluid.

In this study, we surveyed the location of underground station entrances in wards of Tokyo and investigated the circumstances of buildings that are connected to underground station entrances and determined the characteristics of the connections. Result shows (1) the year of installation and the connection form for buildings with office and store uses, the percentages of the connection type and composite type I have increased since 2001, and (2) developments that applied the urban development guidance system since 2001 resulted in the formation of high-quality underground spaces integrated with underground stations.

Data centres are important information and communication technology infrastructures, which are fundamental to the development of the digital economy and smart city in Hong Kong. The increasing popularity of the latest technological applications drives the continuous market growth of data centres in Hong Kong. While there is a surging demand for data centres, land resources in Hong Kong are scarce due to the abundance of hilly terrains. Therefore, it is imperative to explore alternative development solutions to create spaces in addition to searching for available surface land. Numerous successful examples around the world have demonstrated that caverns are highly suitable for the development of data centres. These examples show that there are unique benefits, such as excellent security and stable environments, to house data centres in caverns. Nevertheless, there was no such precedent in Hong Kong. In the light of the above, a conceptual design scheme has been formulated to illustrate the planning and engineering considerations of housing a high-tier data centre in caverns, with due consideration of the geographical settings and technical requirements in Hong Kong. The paper will discuss the special technical considerations of the conceptual design scheme, including the site selection, cavern layout and design, space utilisation, energy efficiency, fire safety strategy, power supplies, operation and maintenance issues.

Hong Kong has a mountainous topography, and there is an acute shortage to meet the demand on readily available land. To accommodate suitable facilities in caverns, such that surface land can be reserved for the most deserving and beneficial uses, the Government of the Hong Kong Special Administrative Region (HKSAR) is implementing two projects at the ex-quarry site at Anderson Road to construct the Public Works Central Laboratory (PWCL) and the Archives Centre (AC) in caverns. These projects have to be executed in a fast-track programme for completion within 5 years’ time. The urgency arises from the planned rezoning of the prime harbourfront land, where the existing PWCL is located, to residential and/or other beneficial uses. On the other hand, the storage capacities at existing achieves facilities have long been exhausted and there is a genuine need for new facility to house the valuable archives. Multipronged measures are thus adopted in the implementation programme in order to meet the challenged timeline. The two projects are packaged as a joint cavern development (JCD) that will provide synergy on the planning, design and construction. Modular Integrated Construction (MiC) is specified in the contract for building the facilities inside the caverns. In the light of the pioneer use of MiC method within caverns, involvement of potential contractors at the early stage of tendering process was arranged to enable practical construction solutions be incorporated in contract. Upon completion, the JCD will be ranked amongst other worldwide cavern projects of accommodating similar important facilities of such scale.

Hydrogen storage is expected to play a crucial role in future power and energy balancing. One proposed method is the use of lined rock caverns (LRC). During the construction of the LRC demonstration plant in Skallen, Sweden, field displacement monitoring revealed noticeable anisotropy. However, a discrepancy was identified between the monitored and calculated convergence obtained from the previous simulations, which were limited to two dimensions and did not consider the presence of joint sets in the rock mass. This paper is to examine the impact of different joint sets on the deformation behavior around the LRC during the construction phase using a 3D model. The results demonstrate that the presence of joints with varying orientations has diverse effects on the symmetric characteristics of the deformation pattern and the degree of anisotropy in the deformation magnitude. The findings enhance the understanding of the deformation behavior of LRC in jointed rock masses and provide insights for identifying the critical joint set(s) through model calibration.

The appearance of cracks in underground concrete structures may lead to a decrease in various performance aspects, such as structural safety, applicability, and durability. From a numerical simulation perspective, it is crucial to carry out cracking and post-cracking mechanical behavior simulations of engineering structures. Among many numerical methods, the phase field model has significant advantages, with its primary feature being the need to refine the mesh in local areas to ensure the accuracy of the phase field simulation results. Based on the unified phase field theory, this paper proposes an adaptive multi-scale analysis method suitable for fracture analysis of underground concrete structures. Firstly, the problem domain is discretized using a coarse mesh, and phase field damage calculation is conducted to obtain an approximate crack damage zone area and derive the damage path. Subsequently, the geometric automatic encryption method is used to locally refine the elements on the damage path. An iterative calculation can be used to obtain a more accurate crack propagation path based on the finely refined local–global calculation mesh. The proposed method features a simple principle, convenient numerical implementation, and strong robustness. It can achieve accurate refinement and multi-scale analysis for complex underground concrete structures. Several typical underground concrete structure examples demonstrate and verify the feasibility and advantages of the proposed method.

Subsea tunnels are of great significance for alleviating traffic pressure. However, the notable change of water level under the action of tide inevitably leads to the re-distribution of rock stress and pore pressure. Therefore, understanding the influence of water level change on the stability and failure response of surrounding rock is crucial for ensuring the safety and stability of subsea tunnels during construction. In recent years, the Material Point Method (MPM) has been gradually applied to large deformation geotechnical engineering problems because it can avoid grid distortion. This study proposes using Material Point Method to analyze the damage response of the water level change to the surrounding rock, based on the engineering background of Qingdao Jiaozhou Bay Second Subsea Tunnel. Considering the water level change under different surrounding rock grades, the distribution principle and characteristics of ground settlement, surrounding rock de-formation, and plastic damaged zone are discussed. The results show that the change in water level is not the decisive factor in the stability of the surrounding rock. Instead, coupling the water level change with the poor rock quality and tunnel design is the key to tunnel failures.

The paper presents the methodology and examples of diagnosing the condition of emergency man-made underground fences in St. Petersburg (Russia). Diagnostic methods are crosshole acoustic and ultrasonic sounding from holes or embedded tubes. The investigation uses crosshole sounding apparatus APZ-1 developed by LLC “Geodiagnostika.” The results of determining the condition of the ice wall of the escalator tunnel of the Zvenigorodskaya metro station, the soil–cement fence of the sewer shaft and the concrete slurry walls of the road half-tunnel in Western High-Speed Diameter are considered.

The advanced geological forecasting method in a tunnel is to determines abnormal geological structures ahead of the excavation face and provides guidance for the construction and the early alert of sudden geological disasters. Utilizing seismic wave reflection is an implementation for advanced geological forecasting, which generally excites seismic waves by explosives and receives signals from sensors placed in the surrounding rock. However, most research ignores the mechanical processes of blasting and directly uses the Reckoner wave function as a point source. As regards the complex explosion mechanism and rock mass, the study aims to explore the propagation and reflection of blasting waves in the rock mass around the tunnel. First of all, an infinitely large soil model with spherical charge blasting is established based on LS-DYNA, and numerical results are compared with the analytical solution to verify the accuracy and validity of the numerical simulation. Then, the 3D structure-geology tunnel model is built, and the explosion and blasting-wave propagation are simulated. After that, an analysis is conducted on the propagation law of blasting stress waves and the change in vibration velocity of the surrounding rock when there is a reflective boundary and no reflective boundary in front. In conclusion, this research contributes to advancing tunnel geological forecasting by considering the mechanical processes associated with blasting and investigating the behavior of blasting waves in the rock mass. This offers the potential for utilizing seismic waves generated by tunnel blasting directly for geological exploration purposes.

Understanding what lies below the ground surface and what condition the ground itself is in is vital for the development of urban underground spaces. As the subsurface is not visible, several geophysical sensing technologies exist to look through the ground. One of these technologies measures variations of gravity but is limited by its sensitivity and relatively slow mode of operation. To overcome this, quantum technology (QT) cold-atom gradiometers have been successfully demonstrated for underground cartography in a field environment. These novel sensors require testing in controlled environments whilst benchmarking them against existing technology. This paper presents a feasibility study on using a gravity gradient sensor in a controlled, large-scale monitoring test using the National Buried Infrastructure Facility ( www.birmingham.ac.uk/nbif ) at the University of Birmingham, UK. Over a 30-minute period, a 3 m3 reservoir was drained of water resulting in a drop of 98 ± 32 Eotvos as measured by two Scintrex CG6s in gradient configuration.

Underground anomalies (e.g., limestone cavities and unknown pipes) have been reported globally in urban areas, which may hinder underground construction and increase safety risks.

Currently, urban traffic poses numerous inconveniences to human beings, including vehicle emissions, traffic congestion and accidents. These issues seriously jeopardize people's health and safety. Therefore, the future development direction of cities revolves around promoting urban decoupling and reshaping the urban framework. One author has proposed a futuristic urban model consisting of three layers of spatial structure. This model enables the separation of pedestrians and vehicles, ensuring pedestrian safety while alleviating traffic congestion. In this research paper, the traffic space incorporates a design featuring wall-mounted air ducts. These air ducts effectively extract and collect vehicle exhaust from underneath the traffic space. Through forced convection, the exhaust is then discharged, avoiding any adverse impact on the surrounding environment. To evaluate the efficacy of this design, 3D models of modern and future urban traffic spaces are created. The study investigates the influence of various factors such as vehicle exhaust emissions (number of cars), environmental wind speeds, air distribution modes and duct layouts on the temperature field and exhaust distribution within traffic spaces. By comparing the results obtained from the two urban models, it is determined that the utilization of wall-mounted ventilation ducts effectively removes vehicle exhaust from the traffic space, preventing its negative effects on the surrounding area.

The HSS model is often used for excavation analysis because of its excellent performance in modeling the small strain behavior of soil. The reliability of the numerical analysis using the HSS model depends on high-quality soil parameters. However, obtaining undisturbed samples for sands, silts, and muddy clay is difficult. This paper presented a numerical simulation of a subway station excavation located in the Yangtze River floodplain area of Nanjing. The subway station is surrounded by thick soft clay, and it is difficult to obtain high-quality samples. A SCPTU-based method was proposed to determine the HSS model parameters of soft clay. Since the SCPTU test is conducted in the in situ stress state, it overcomes the problems of sampling disturbance. The soil parameters obtained by the SCPTU test were used to calculate the excavation-induced lateral wall movements through numerical analysis. The numerical analysis results were compared with the measured values, and those obtained by numerical analysis which the soil parameters were calculated by soil compression modulus. It was found that, after excavation, the numerical simulation results based on the SCPTU test are consistent with the measured values. However, the simulated maximum lateral wall movement is only 53% of the measured value. The SCPTU-based parameters are more reliable than those based on soil compression modulus.

This study presents key technologies for the safe construction of underwater super large diameter shield tunnels based on the engineering of Zhuhai Shizimen undersea super large diameter shield tunnel. A comprehensive introduction is carried out from three aspects of safety construction technologies, disaster optimization design and rapid disease detection. This discussion delves into high durability requirements, tunnel detection difficulty and high seismic risk for underwater super large diameter shield tunnels. And then a series of key technologies was proposed to solve the problems of the underwater super large diameter shield tunnels faced. And the application of these key technologies in Shizimen tunnel is introduced in detail. Finally, a summary of current intelligentization and automation in underwater shield tunnels was offered. The future trends of development in underwater shield tunnels are also introduced. The current overall gaps in underwater shield tunnels concerning sustainability and environmental protection are identified in an attempt to stimulate further work in these areas by the research community.

Site soil shows anisotropic behavior due to its structural characteristics, formed in the prolonged sedimentation process. For more efficient utilization of underground space, reasonable and proper description of soil anisotropy is a crucial step in simulating complex geological conditions, which is helpful in assessing the excavation safety and its impact on the surrounding environment. This study analyzed a well-recorded excavation case through finite element analysis, adopting an advanced soil constitutive model simulating the anisotropy behavior of clay. The necessity of restoring the natural soil characteristics was highlighted, due to the underestimated deformation prediction resulted from soil isotropic hypothesis. In more detail, this study also analyzed the features of excavation and supporting between two different construction sequences, namely top-down and bottom-up methods. Differences of retaining structures’ deformation modes and the influences on adjacent infrastructures were also identified. Suggestions were proposed for the sake of safe construction and reasonable cost.

We evaluated the stress-dependent permeability of sawcut granite fractures grouted with chemical and biological agents, with and without quartz sand mixture. The permeability of chemically grouted fractures is more affected by confining pressure than biologically grouted fractures. The addition of quartz sand reduces the dependency on stress for both the grouted fractures.

Serpentine tailings could be used as a low-carbon binder to replace Portland cement. This paper developed a novel technique of foamed concrete using serpentine tailings, reactive magnesium oxide (RMC), and carbon dioxide (CO2) foams, so called serpentine carbon sequestration foamed concrete (S-FC). The technology enhances the carbonation efficiency and mechanical performance of MgO-based materials by combining a foaming agent with CO2 curing. Six sample groups were prepared to investigate the impact of serpentine proportions on the mechanical behavior and microstructure of S-FC. Hydration of serpentine and RMC was evaluated by isothermal calorimetry. Compressive strength results were used to assess the mechanical performance of SC-FLS samples. Quantification of hydrate and carbonate phases was conducted via XRD and TGA to examine the potential of SC-FLS in carbon sequestration. An optimal design was determined for serpentine content by the combination of the above tests. Results highlight the capacity of SC-FLS to sequester CO2 actively.

Singapore has at least two known hot springs with surface water temperatures of 50–90 °C. Together with its estimated high heat flow, Singapore is thought to have a geothermal potential. To assess the potential, we focus our study on the northern part of Singapore, where elevated shallow subsurface temperatures have been identified. Two deep exploratory slimhole sites are selected within this region. One slimhole has been successfully drilled to a record-breaking depth of 1.1 km within Singapore’s granite bedrock at Admiralty Lane. Subsurface temperatures are measured, and rock core samples are collected from this slimhole. Data analysis reveals a high geothermal gradient at depths beyond 800 m, surpassing the global average continental geothermal gradient. If this temperature gradient remains constant beyond 1.1 km deep, the rock temperature at 4–5 km deep can be estimated to reach 200 °C. The temperatures are found to be hotter than many other non-volcanic regions around the world. Additionally, laboratory measurements on the rock core samples found that the granite at the Admiralty Lane site, also known as the Simpang granite, has an above-average radiogenic heat production, that if consistent to over 10 km deep, can contribute significantly to Singapore’s anomalously high heat flow. The study to date finds that Singapore’s Simpang granite has high geothermal gradient, heat production, and heat flow. These findings underscore Singapore’s promising geothermal potential, warranting further exploration to deeper depths, such as 5 km. This journey could unlock opportunities for sustainable energy initiatives.

Optimizing geothermal heat extraction requires a deep understanding of the thermal properties of host rock. This study identifies the governing factors to enhance heat extraction rate and efficiency under various geological and operational conditions, using both water flow experiments and 3D numerical models. Our results indicate that the surrounding temperature and flow rate significantly affect the heat extraction rate and efficiency.

Singapore is exploring potential geothermal reservoirs to reduce its reliance on natural gas and transition towards sustainable energy sources. With only 4% of registered power generation capacity coming from renewables, the city-state aims to achieve net-zero emissions by 2050. The study focuses on harnessing low- to medium-temperature geothermal resources for electricity generation using organic Rankine cycle (ORC), which is a heat-to-power conversion technology. The simulation results project that each Enhanced Geothermal System (EGS) well doublet has an electrical generation capacity of 0.93 MWe, equivalent to about 7 GWh annually. This EGS-ORC system can be scaled up to exploit the heat within Singapore’s granite. Furthermore, the study conducts comprehensive analyses, employing Life Cycle Assessment (LCA) and Life Cycle and Cost Analysis (LCCA) methodologies. LCA reveals that geothermal electricity's global warming potential is significantly lower than Singapore’s current grid emission factor. LCCA estimations show the net-present levelized cost of electricity is competitive with Singapore’s long-run marginal cost and aligns with the Uniform Singapore Energy Price. The rejected hot fluid from the geothermal system can further enhance its economic viability. The study offers valuable insights for urban planners, policymakers, and researchers in Singapore's transition towards resilient and eco-conscious energy systems.

It has long been pointed out that the basic guidelines in the form of an underground utilization master plan and underground utilization policy are necessary for the effective utilization of urban underground spaces. Therefore, the Urban Underground Space Center of Japan (USJ) organized a subcommittee to investigate relevant cases in Japan and overseas to confirm the necessity for the formulation of the basic guidelines. In order to prepare the guidelines, we presented a proposal to discuss what topics should be included and how to organize the guidelines. The results thus obtained are summarized as preliminary for the guideline (draft). In addition, we chose a model district urban development in which underground space is assumed to be utilized, and at the same time, we checked on the adequacy as a guideline. As a future topic, it is confirmed that the guideline should have the consistency with various relevant systems and its applicability to the master plan for the underground development. This report summarizes the results of this research.

Being a complement to ecosystem services (ES), geosystem services (GS) is a novel concept that helps identify and understand the contributions of the diversity of geological structures and processes of nature to human wellbeing. A pilot survey was carried out to Swedish municipalities in order to: (i) in a systematic way investigate if and how they currently approach GS in their spatial planning processes, and (ii) analyze and follow up responses for further improvement of the questionnaire for a Sweden-wide survey. None of the ten out of 26 responding municipalities currently use the term GS in their spatial planning processes. Some GS are already considered in municipal spatial planning processes in Sweden, though the term GS is currently not used. No clear patterns of including GS in spatial planning were however observed, except for three out of twenty GS. Social and child impact assessments and the Swedish standard on Biodiversity survey, which were the most frequently used methods for including ES in the municipal spatial planning processes in Sweden, could potentially be extended to GS.

Underground space (UUS) use is of great importance for sustainable urban development. However, it is far from persuasive to compare the descriptive values of UUS with the construction costs. The value of UUS use to urban sustainability shows both positive externalities and negative externalities. The lack of quantitative value analysis might result in a “radical” or “conservative” mode of UUS development. In this regard, the quantification of UUS value, particular the external value in monetary terms, will become the turning point in the planning and land administration process of UUS development. This short article gives a brief introduction of a series of studies that monetize and visualize the externalities of UUS use to urban sustainability based on the service replacement cost method while using UN 2030 Sustainable Development Goals (SDGs) as value metrics. The valuation results are utilized to establish a set of new approaches for sustainability-oriented UUS development strategies of planning evaluation and land price setting.

Metro-led underground space (MUS) use has gained unprecedented popularity in China over the past decade. Empirical studies indicated that the development of MUS, which primarily aligns with transit-oriented development, is likely to boost urban vitality, enhance spatial efficiency, and optimize spatial configuration. However, the development regularities remain unclear for MUS in high-density built environment of Chinese cities, resulting in a lack of theoretical foundation for MUS planning. To bridge the research gap, we adopted a set of spatial statistics techniques and formulated a quantitative indicator system to decipher the underpinning patterns of MUS use based on multisource big data. We probed into the driving forces of MUS in China at multiscale from a spatiotemporal perspective. Finally, the driving patterns of MUS in different spatiotemporal conditions were identified and compared in a systematic manner. The study provides insights into the increasingly growing MUS use, and supports the optimization of planning theory for MUS in China.

Kosancicev Venac represents one of the most important and most sensitive urban complexes of old Belgrade, which in the chronology of urban development represents the oldest conserved part of the city with a spontaneously developed urban matrix. One of the characteristics and specifics of the area of the Kosancicev Venac is the presence of underground lagums from the mid-eighteenth century. By following the requirements and measures of conservation and preserving the monument status of the area, a planning solution was made, with the aim of preserving, affirming, and improving the area, protecting the public interest, making conditions for creating new values regarding surroundings to include cultural, historical, and architectural heritage into the modern development of city life. The significant goal of the Plan is the inclusion of historical underground areas and tunnels in the planned public uses on above-ground surfaces and building foundations of the affirmation of Belgrade’s underground spaces as a tourist potential. By adopting the Plan, the conditions have been met for realization of capital facilities of public use in culture and higher education and designing the areas in public use according to the highest standards of urban, architectural and landscape design, and repurposing lagums, which are part of the history of Belgrade, for contemporary uses.

Carbon reduction has become a critical issue for urban infrastructure. The application of information technologies (ITs) in LCBs has greatly improved their carbon reduction capacity and service level. However, ITs’ application in low-carbon tunnels (LCTs) has been limited. This study offers insight into how to develop LCTs using emerging ITs to enable more socioeconomic and environmental benefits. The paper reviews 173 pieces of literature on how ITs serve the life cycle of LCBs. The obstacles faced by ITs in contributing to LCBs are also discussed. By analyzing the differences between buildings and tunnels, we draw on the development experience of LCBs to provide suggestions for ITs’ application in LCTs. This study would help researchers and policymakers working on LCTs with a clear perspective of current work and research gaps in this area, thus facilitating carbon reduction and sustainable development of tunnels.

The scope of geotechnical investigations in tunnel projects is generally driven by allocated resources rather than the expected ground variability. This research proposes a systematic and rational methodology for identifying priority locations of geotechnical investigations based on tunnel risks, site conditions, and project-related constraints. The methodology is applied to an actual soil tunnel project in an urban setting using preliminary geotechnical investigation data. The goal is to quantify the spatial uncertainty in soil abrasivity index (SAI), which is a geotechnical parameter that influences the risk of cutter tool wear. Stochastic geostatistical modeling algorithms are utilized to characterize the 3D spatial variability in soil units and SAI. Geospatial visualizations of SAI uncertainty and consequences of tool wear are employed to develop an R index map that highlights the impacts of uncertainty in tool wear rates. Project constraints such as drilling accessibility and budget are integrated into the R index map to identify priority locations for additional investigations. The study involves virtual sampling of additional boreholes to quantify the uncertainty reduction in tool wear rates and the locations where intervention by the tunnel boring machine (TBM) may be required. The results show that prioritized investigations targeting areas with high ground uncertainty can reduce the uncertainty in intervention locations by approximately 90 rings (equivalent to 160 m).

Shield tunnelling is a complex and challenging process that is prone to risks. This study proposes a novel risk assessment framework on the basis of geological conditions and shield parameters to enhance the safety and efficiency of tunnelling. The proposed framework integrates the multi-grained cascade forest (gcForest) and fuzzy set pair analysis (FSPA). The former is utilized for the prediction of shield operational parameters based on the geological conditions, while the latter is employed to assess the risk level based on the data characteristics of predicted operational parameters. The objective weights used in the FSPA are obtained from the intercriteria correlation. A case study of a field tunnel project in Guangzhou is conducted to validate the assessment framework. The results indicate that the predicted risk levels agree well with the real engineering observations. The proposed framework is a practical tool for assessing risk during tunnelling, contributing to improved project management and risk mitigation.

Underground excavation has a long history of using bio-inspired technologies to tackle engineering challenges, such as tunnel boring machines. Recent studies show amazing discoveries of rock-burrowing bioerosion by smart organisms in the marine and freshwater environments of Southeast Asia countries (e.g., Myanmar and Philippines). The newly discovery of rock burrowing strategies inspired by bio-erosion is based on the concepts of utilizing chemical etching to weaken calcareous substrates by removing dissolvable minerals and subsequently applying the remaining hard mineral grains to break down the weakened rock and accelerate the burrowing operation. A series of direct-shear tests were performed on intact limestone-smooth steel interface, chemically treated limestone-smooth steel interface, intact limestone-quartz-coated steel interface, and chemically treated limestonequartz- coated steel interface. Our results demonstrate that the chemically treated limestone—quartz-coated steel interface has the lowest friction angle and the most serious damage on the limestone surface during the tests. The results confirm the efficiency of bio-inspired burrowing strategies, comparing to the results obtained from the other interfaces, and reveal the combination of chemical etching and mechanical abrasion promotes rock material breakability while maintaining low energy consumption.

In this study, a series of trapdoor tests were conducted in sand in an existing circular tunnel. Digital image correlation (DIC) was used to visualize the displacement and shear information of the sand. The effect of the backfill burial depth was considered. The results showed that the same load–displacement curve characteristics can be obtained with four stages (initial arching, maximum arching, load recovery, and ultimate stages), whether an existing tunnel is present or not. The ultimate soil arching ratio is degraded in ground with a tunnel, and most evident with H/B = 4.0, compared to the results without structures. The shadowing effect of existing tunnels is significant. A shield region was generated above the existing tunnel. The shear band gradually expanded from the inside to the outside as the trapdoor slid downward. New shear bands formed at the tunnel shoulder when the shear band exceeded the trapdoor width range. Two deformation patterns, parallel flow over a tunnel and cross-flow over a tunnel, were identified based on development of shear bands in the sand within the existing tunnel.

Groundwater is a critical determinant significantly affecting the stability of underground tunnels. Despite its importance, research remains limited on the influence of groundwater level fluctuations on the behavior of rectangular tunnels. This paper addresses this knowledge gap by thoroughly examining the response mechanism of rectangular tunnels subjected to groundwater level fluctuations, utilizing a combination of scale model tests and numerical simulations. The study emphasizes the analysis of the effects of varying buried depth ratios and speeds of groundwater level fluctuations on the performance of rectangular tunnels. Findings indicate that changes in groundwater levels result in the vertical displacement of the tunnel and instigate deformations in the surrounding soil. Moreover, alterations in hydraulic conditions considerably shift the stress and strain distribution within the tunnel, with stress concentration becoming increasingly evident as the tunnel's buried depth ratio and the speed of groundwater level fluctuations increase. The insights derived from this study offer valuable contributions for future research efforts and engineering design in the domain of rectangular tunnel stability under fluctuating groundwater conditions.

The subsurface space is complex—it contains a myriad of buried assets (e.g. pipes and cables) and transport infrastructure (e.g. tunnels) which form the backbone of our modern society. The ground provides the support both for the surface infrastructure as well as the subsurface infrastructure—indeed, it is an asset in its own right. However, it can vary both spatially and temporarily making the subsurface system complex. At the same time, the underground space is a huge resource which can be used in variety of different ways, e.g. housing of hard infrastructure to free up surface infrastructure, provide a renewable source energy as well as furnish water storage and supply. New technologies and construction methods are constantly developed to operate in, see through or construct within the subsurface. Objectively evaluating these new approaches can often be challenging as access to field trials can be complicated and these often lack the required control and knowledge of the ground truth. The newly opened National Buried Infrastructure Facility (NBIF, www.birmingham.ac.uk/nbif ) situated at the University of Birmingham, the UK, enables full-scale or nearly full-scale controlled testing.

Accident breakage of unknown utilities (e.g., cables and pipes) frequently occurs during underground construction and causes temporary cut-off of energy and water supplies in urban cities. Mitigation of the excavation risks requires fast and accurate detection of subsurface utilities, but the current geophysical methods suffer from high computational cost and human subjective judgement. Here we developed a data mining method for fast detection and location of underground utilities from the collected data using the seismic scattering theory. The detection of underground utilities is based on analyzing the differences in relative energy levels of effective signals among various seismic records that are generated by a moving seismic source. Specifically, when the position of a seismic source is close to underground utilities, the energy of effective signals increases. The increased intensity is proportional to the size of the utility. The energy change is captured using data mining algorithms including scale analysis and low-rank feature extraction. Finally, underground utilities can be identified by a larger anomaly score which is defined by the energy of extracted effective signals. The effectiveness of the proposed method has been demonstrated by testing on field underground water pipes detection.

A deep exploratory slimhole reaching a depth of approximately 1.1 km was successfully completed in the northern part of Singapore. The rock cores extracted from the exploration slimhole provide a unique opportunity to understand rock conditions past few hundred metres deep and generate datasets such as overall rock conditions and concentrations of various elements. Good-quality rocks are seen in most of the rock samples with coarse-to-medium-grained minerals. The rock cores are found to be lightly fractured and jointed. Hydrothermal alteration, as observed in rock cores at various depths (e.g. 500 m and 670 m), destroyed the original granitic texture. The rock cores have averaged heat production values of around 5 μW⋅m−3 throughout the borehole. Two zones of very poor rock quality are observed at around 565 m and 1.1 km deep. The rocks at both weak zones are found to be extremely weak, highly weathered and brecciated, contain specular hematite filling, and have low heat production of around 3.5 μW⋅m−3. The second and deeper weak zone consists of a continuous zone of highly weathered and altered fine sand to pebble-sized rock fragments exhibiting a potential cataclastic texture. Here, heat production values are observed to be around 1 μW⋅m−3. Highly altered and weathered rocks within these weak/porous zones indicate fluid-rock interactions. However, their vertical and lateral extents are not well constrained and should be investigated further. If similar zones are found at greater depths, they could be utilised as natural conduits for fluid circulation to extract heat from hot rocks, thereby reducing the potential need for rock fracturing.