Advances in Rock Mechanics—Infrastructure Development, Volume 2

Inhaltsverzeichnis

1. Frontmatter

2. Evaluation of Flattened Brazilian Disc Test to Analyze the Indirect Tensile Strength of Rock

   Manali Sarkar, Arindam Basu

   Abstract

   Rocks are weaker in tension. Therefore, the estimation of tensile strength is crucial in any rock engineering environment. The Brazilian disc test is the most conventional method carried out to evaluate the indirect tensile strength of rock. However, the problem of fracture initiation in Brazilian discs has been a topic of concern for several researchers. High shear stresses tend to develop at the platen-specimen contacts leading to initiation of fracture at the contact. Eventually, researchers suggested plane loading of Flattened Brazilian Discs (FBD) to solve the issue. This modification is done by flattening two diametrically opposite ends of the disc. In FBDs, it is theorized that the crack initiation originates at the center if the loading angle subtended by flat ends (2α) is ≥19.5°. Most of the work regarding FBD specimens is numerical in nature, and a comprehensive experimental evaluation does not seem to have been taken up by previous researchers. Nearly all the numerical analyses assume homogenous and isotropic specimens which are far from reality. Moreover, almost no study has been done on the influence of the strain rate or deformation rate on FBDs. This study investigates the tensile behavior of FBD specimens using granite when loaded under deformation rates of 0.5 mm/min, 1.5 mm/min, and 5.5 mm/min. The loading angles (2α) considered for experimentations are 10°, 20°, 30°, and 40°. The failure patterns are also observed and analyzed.

3. Development of Tunnel Face Observation Method on VR Space and its Application

   Moeru Kojima, Shuntaro Miyanaga, Kazuo Sakai, Masahito Yamagami

   Abstract

   Observation of tunnel excavation faces is one of the crucial tasks for ensuring safe construction. Photographs of the faces sometimes complement geological engineers’ visual investigation; however, they are insufficient for a comprehensive geological assessment. Instead of the conventional methods, we have developed a method for observing tunnel faces in virtual reality (VR), using visualization of 3D point cloud data with a customized software. Two types of manual strike and dip orientation measurement functions for discontinuities have been implemented in the software. To validate its effectiveness, we applied the method to tunnel sections where weathered and altered andesite and talus deposits were distributed. The method identified unconformities at the bottom of the talus, which were unclear from photographs alone. Moreover, the measured strike and dip data quantified the geological structure of the unconformity. From these results, we conclude that the VR observation is more effective for detailed geological evaluation than the conventional 2D photographic methods.

4. Shear Strength and Deformation Failure Characteristics of Sandstone Under True Triaxial Stress Shear Tests

   Liang Hu, Jun Zhao

   Abstract

   Shear failure is a common phenomenon in deep engineering works, affecting both intact and structural rock masses. In particular, under high true triaxial unequal stresses (σ₁ > σ₂ > σ₃), rocks exhibit significant disparities in the deformation, shear strength, and failure characteristic. However, the shear strength and deformation failure characteristics of rocks under true triaxial unequal stress remain unclear. In this work, the shear test apparatus was used to undertake true triaxial shear tests under different stress conditions. The shear deformation failure and strength of intact sandstone were investigated. The test results show that dilation in the normal direction and compression deformation in the shear direction. The normal stress plays a significant role in the shear deformation of intact sandstone. It is important to note that normal stress exhibits a positive correlation with shear strength and shear stiffness, whereas the effect of lateral stress on these parameters displays variability. Specifically, lateral stress exerts an influence on rock strength by modulating its internal structure. Furthermore, lateral stress may elevate the propensity for ductile fracture within the shear rupture zone, thereby mitigating brittle fracture in the rock.

5. Fundamental Study of Lining and Road Maintenance Management of In-Service Road Tunnel Combined 3D Point Clouds and Life Cycle Data

   Hiroyuki Honda, Trissha Anneta, Hisatoshi Taniguchi, Yasuhiro Mitani

   Abstract

   Monitoring the deformation of the road surface and the concrete lining is indispensable to verify the tunnel’s structural integrity in the maintenance and management of mountain tunnels. Detecting and understanding these deformations are crucial to ensure the tunnel’s safety and usability. Any observed deformation could indicate potential structural issues, necessitating early detection and appropriate countermeasures. Recently, Terrestrial Laser Scanner (TLS) has been used in tunnel construction projects, which can obtain 3D point cloud data by irradiating and scanning an object with a laser. However, more practical application is needed in maintenance management.

   This study focuses on in-service road tunnels constructed in the 1990s and attempts to identify deformations of the road surface and lining surface by scanning the inner of the entire tunnels every year since 2017. As a result of the scan, we grasped the micro deformation of the road surface and lining. In addition, by combining 3D point cloud data and regularly collected images of lining inspection, it was possible to evaluate the cause of cracks on the surface of lining concrete. Furthermore, we revealed the possibility of effective and efficient maintenance management by integrating with the life cycle data.

6. A Study on the Relationship Between the Mechanical Properties and Wave Propagation Characteristics of Fractured Rock Under Shearing

   Zheng-Yi Cai, Hung-Hui Li, Hoang-Khanh Le, Meng-Chia Weng, Chia-Hao Ku, Chih-Chun Chien

   Abstract

   Rock masses often exhibit intricate weakness planes that often interconnect to form an impenetrable rock bridge, potentially impacting the stability of the rock mass. To understand how fractures develop under sustained shear stress and whether changes in the wave propagation characteristics can reflect the mechanical behavior of fractured rock, this study integrates direct shear tests on fractured rock specimens with ultrasonic measurements. By analyzing the shear stress–shear displacement curves and wave velocity variations obtained from the mechanical tests, preliminary insights into the relationship between initial failure behavior and crack development before reaching the peak shear strength of the rock mass have been gained. The following findings are obtained: (1) The initial failure shear strength (τ_i) was approximately 0.5–0.7 times the peak shear strength (τ_p), and the initial failure shear displacement (s_i) was approximately 0.5–0.6 times the peak shear displacement (s_p). (2) As the length of the rock bridge increased, the initial failure shear strength (τ_i), the initial failure shear displacement (s_i), and the peak shear displacement (s_p) also increased.

7. Evaluation of the Influence of Temperature on Physico-Mechanical Properties of Intercalated Shale-Sandstone

   Rishimon Munshi, Arindam Basu

   Abstract

   The physico-mechanical properties of rock materials are generally affected by temperature variations. The changes in the behaviour of the rock material would depend on several factors, for instance, the rate and duration of thermal exposure, the state of stress, and the mineral composition. Earlier investigations by various researchers established the physico-mechanical behavioural changes of massive and anisotropic shale and sandstone individually under varied thermal exposure. However, the properties of intercalated shale-sandstone as a composite material appear not to have been thoroughly assessed. Therefore, the core aim of this study is to analyse variations observed in the physico-mechanical properties of intercalated shale and sandstone before and after exposure to different thermal conditions. To accomplish the objective, the core specimens of intercalated shale-sandstone (from Korba, Chhattisgarh, India) were divided into different sets. Each set was treated with cycles of varying temperature conditions, such as low- and high-temperature thermal shock as well as freeze-thaw. Furthermore, to assess the mechanical properties, the treated specimens were subjected to the Brazilian test to determine the tensile strength. Both the physical and mechanical properties were recorded at an interval with progressing cycles. The test results were compared and comprehensively analysed.

8. Transformer-Based Surrogate Model for the Optimization of Geological Carbon Sequestration

   Zhao Feng, Weiquan Ouyang, Zeeshan Tariq, Zhilei Han, Xianda Shen, Bicheng Yan, Fengshou Zhang

   Abstract

   The optimization of well controls and perforation locations constitutes an essential procedure in geological carbon sequestration (GCS). Such optimization tasks can be computationally intensive due to the need for many forward simulations. This paper presents a novel transformer-based deep learning neural network as a surrogate model to accelerate the optimization process. Transformer layers are utilized to efficiently capture the temporal dynamics via the self-attention operation. The spatial temporal evolution of CO₂ plume is predicted in parallel. Results show that the surrogate model can produce decent accuracy (R² > 0.99) and offer a speedup of at least 80,000 times compared to numerical simulation. The proposed model is further integrated with the Particle Swarm Optimization (PSO) algorithm for the determination of well controls and perforation locations. The trapped CO₂ volume and sweep efficiency are optimized. The proposed methodology significantly reduces the computational expenses of optimization tasks and provides a promising approach for GCS project management.

9. The Thermo-Hydro-Mechanical Coupled Phase-Field Modeling of Hydraulic Fracturing in Deep Hydrocarbon Exploitation

   Hanzhang Li, Fengshou Zhang, Yuhao Liu

   Abstract

   With the gradual depletion of hydrocarbons (oil and natural gas) in shallow reservoirs, the exploration and exploitation of deep underground reservoirs has become a necessity to ensure an adequate energy supply for the society. The deep reservoirs are characterized by high in situ stress and relatively high temperature. In this work, we propose a thermo-hydro-mechanical (THM) coupled phase-field model and verify its accuracy with benchmarks. The effects of in situ stress and temperature are taken into consideration. A staggered scheme and a fixed stress-split method are employed to solve the coupled THM equations. Simulations of hydraulic fracturing on single injection well models, and then multi-well models are implemented in the open-source FEM package OpenGeoSys. On single injection well models, the hydraulic crack grows longer when a higher in situ stress difference (difference between the maximum horizontal stress and the minimum horizontal stress) is applied. The effect of temperature is mainly reflected on the hydraulic crack characters such as length and width. Numerical results from multi-perforation models show that the heterogeneous pressure induced by depleted production wells can affect the hydraulic crack growth path, causing limited hydraulic crack length. Meanwhile, the simultaneous fracturing of multiple perforations results in competition and suppression of crack propagation between adjacent perforations.

10. Smartification and Accuracy Verification of Long-Term Survey Method Using Tunnel Excavation Blasting as Seismic Source

    Masahito Yamagami, Shyuntaro Miyanaga, Kazunori Murata

    Abstract

    In mountain tunneling, it is important from the point of construction safety and effectiveness to obtain information on the weak zones such as fracture zone ahead of the face, which may pose problems during construction. To provide long-term outlook for tunnel work without disturbing excavation, the authors have developed a tunnel seismic reflection survey method known as the Taisei Blast Excavation Prospecting (T-BEP). This method extends the maximum surveyable distance beyond 350 m, doubling or tripling the capability of other conventional methods. However, complicated works are necessary in the preparation and measurement processes, and there are safety concerns. Therefore, we have improved the old T-BEP and developed a new version. In this paper, we present an overview of the new version and report the results of comparative validation experiments between the new and old T-BEPs.

11. Experiences from Application of Empirical and Analytical Methods in Slope Stability Analyses for Weak Rocks on Macedonian Road Network

    Milorad Jovanovski, Bojan Janevski, Igor Peshevski

    Abstract

    This paper presents authors’ experiences gathered from several large infrastructure projects on Macedonian road network. The results of the slope stability assessment using mainly limit equilibrium and empirical methods are presented for over 80 deep cuts composed of Paleozoic schists metamorphic complex or in Eocene flysch sedimentary deposits. The rock masses are usually highly weathered, tectonically disturbed, and often folded with low rock mass quality. They are prone to local or global instabilities deformations expressed as wedge, planar, or rotational mode of failure, depending on local joint set combinations and slope elements. Results are mainly presented in a form of partially modified diagrams from known Q-slope method, where in parallel, values from calculations of Factor of Safety are added. Some elements related to new Eurocode 7 Design Approaches are also analyzed. The key finding is that uncertainties in a final definition of slope geometry comes not only from input parameters, but also from chosen design approach. The best way to assess the stability condition is with a combination of different tools and methodologies, especially when we face highly weathered and weak rock mass formations. Some recommendations for further development of the methodology are also presented, and they are mainly related to possibilities to estimate decreasing of strength properties as important elements for long-term rock slope stability for such rock slopes.

12. Assessment Roughness Anisotropy of Rock Discontinuity Using Photogrammetry

    Tae Hyeon Kim, Hwi Hoon Park, Kwang Yeom Kim

    Abstract

    In rock mass assessment, one of the most crucial factors to consider is the discontinuity, which significantly influences the behavior of the rock mass. Therefore, proper assessment of discontinuity is essential. The roughness of discontinuities is a major property affecting the shear behavior of the rock mass and the flow characteristics of fluids within it. This study analyzed the roughness and anisotropy of roughness of discontinuity using 3D profiles obtained through photogrammetry. Six discontinuities present on the outcrop were selected for the assessment. The 3D model was generated using Bentley software Context Capture, based on multiple digital images taken with a smartphone at different angles. To validate the accuracy of the generated 3D discontinuity profiles, a comparative analysis was conducted between the profiles measured with a profile gauge and the extracted profiles from the generated 3D model. Lastly, the roughness along different directions for each discontinuity was estimated. This analysis revealed that among the six discontinuities, two exhibited a large anisotropy ratio, exceeding 1.3.

13. Convolutional Neural Network-Based Three-Dimensional Rock Discontinuity Trace Mapping and Orientation Characterization

    Sang Seob Kim, Gyung Won Lee, Kwang Yeom Kim

    Abstract

    Ensuring stability and designing suitable excavation and support patterns require precise rock evaluation. Discontinuities in rock are critically considered during rock assessments. This study proposes a method for acquiring three-dimensional trace mapping data using a Convolutional Neural Network and utilizing this data to characterize the orientation of rock discontinuities based on trace data. The three-dimensional trace mapping data is generated using simple image processing method without complex computations. To characterize orientation, Principal Component Analysis is used to calculate the normal vectors of the three-dimensional trace data, which are then used to determine dip and dip direction. The trace mapping results using CNN showed high trace persistence, with minimal omissions. The trace-based orientation characterization results were compared with surface-based characterization, confirming its effectiveness as an orientation characterization method.

14. Remote Sensing and Ground LiDAR Scanning-Assisted Landslide Investigations: Lessons Learned from Example Nearby Southern Cross-Island Highway in Taiwan

    Pai-Chiao Lo, Yong-Zhi Huang, Tai-Tien Wang, Wei-Chia Chu, Hsi-Hung Lin

    Abstract

    Recent rapid advances in surveying and mapping technology can produce sophisticated digital surface models (DSM) in the forms of image and point cloud, which have great application potential to assist landslide investigations. Taking the landslides adjacent to the interface between slate and schist along a highway in southeastern Taiwan as examples, this study uses tools such as close-range photography, UAV-based photography, and ground-based light detecting and ranging (LiDAR) to produce DSMs and point cloud models to assist landslide investigation. The possible application of these advanced surveying and mapping technologies is also discussed. Research results show that the advantages of these advanced technologies include: refined landform variation analysis, assisting surface geological survey, assisting rock mass characterization and related engineering parameters evaluation, and quantifying collapse content through digital elevation model of difference (DoD), which can effectively assist landslide investigation.

15. Exploring the Impact of Point Cloud Model Resolution on Interpretation Results: A Case Study of Outcrop Surveys

    Yong-Zhi Huang, Tai-Tien Wang, Fu-Shu Jeng

    Abstract

    With the advancement of remote sensing technologies, engineers can employ various modeling methods to generate detailed three-dimensional point cloud models. These methods include unmanned aerial vehicle (UAV) modeling, close-range photogrammetry modeling, ground-based LiDAR, etc. Coupled with point cloud analysis, geometric parameters of discontinuity surfaces on outcrops can be obtained, leading to the characterization of engineering properties of rock masses. This technology enables large-scale and efficient quantitative analysis, and there have been numerous successful implementations globally. However, there is a lack of exploration into the impact of model resolution, with most studies merely mentioning resolution in the context of model generation without explicitly addressing its influence on interpretation results. In this study, three different and common modeling methods were employed to create outcrop point cloud models along Highway 20 in Taiwan. This research aims to illustrate and compare the differences in interpretation results among models produced by different methods. The results indicate that close-range photogrammetry produces the highest model resolution, followed by UAV modeling, and ground-based LiDAR with the lowest resolution. Regarding orientation interpretation results, the point cloud percentage distribution on various discontinuity sets is consistently ranked, with dip and dip-direction are mostly falling within the range of ±10°.

16. Hydraulic Fracture Test Simulation Using Three-Dimensional Particle Flow Code

    You-Jie Huang, Tai-Tien Wang, Fu-Shu Jeng

    Abstract

    Hydraulic fracture test is one of the most commonly used measurement methods to obtain in situ crustal stress, which is important information for the earthquake risk assessment and geological resources development evaluation. However, the variation of injected water pressure during a hydraulic fracture test is affected not only by principal stress components to be measured, but also by properties of rock formation such as strength and homogeneity. The scattered measurement results from various hydraulic fracture tests carried out nearby typically generate difficulties in the interpretation of in situ stress. Our study develops a three-dimensional particle flow code for the simulation of hydraulic fracture tests. Rock strength is considered through bonding properties between particles, and the heterogeneities of rock formation can be taken into consideration through varying bonding properties. The injected water seeps through particles and the associated injected pressure accumulated within the spaces surrounding by particles. Simulation results demonstrate that our code is capable of reproducing the characteristics of a pressure curve obtained by a hydraulic fracture test and the development of rock fractures can be compared simultaneously, benefiting the interpretation of measured results and associated explanation regarding scattered results caused by rock heterogeneity later on.

17. Seismic Vulnerability of Underground Structures in Varying Rock Mass Qualities: A Numerical Analysis

    Suresh Raj Kalouni, Harendra Raj Kalauni

    Abstract

    Earthquakes pose significant challenges to the stability and integrity of underground constructions, making an in-depth assessment crucial for enhancing structural resilience. The seismic effects on tunnels within varied rock mass qualities remain a critical concern in engineering practice. Understanding the impact of earthquakes on different rock qualities is imperative for ensuring structural integrity and safety. This study examines the impact of earthquakes on underground structures in varying rock mass qualities (Q) using numerical analysis. The study employs a finite element model to simulate the behavior of underground structures under seismic loading. The model considers the interaction between the structure and the surrounding rock mass, accounting for the influence of rock mass quality on the structural response. The study’s findings reveal that the seismic response of underground structures is strongly influenced by rock mass quality. Structures in lower quality rock masses (lower Q values) experience higher stress levels and deformations compared to those in higher quality rock masses. These findings provide valuable insights into the seismic vulnerability of underground structures and emphasize the importance of considering rock mass quality in the design and construction of such structures in earthquake-prone regions.

18. A Review of Technology Advancement and LiDAR Approach in Subsidence Measurement Method

    Nirmana Fiqra Qaidahiyani, Seokwon Jeon

    Abstract

    Mine subsidence poses significant engineering and economic challenges, emerging as a paramount focus in geo-environmental monitoring. Accurate prediction and assessment of its impact on structures are crucial for designing effective mitigation strategies and ensuring the safety and sustainability of mining operations. Monitoring methods have evolved over time, progressing from traditional ground observation stations to more comprehensive approaches that combine these methods with space-based and aerial technologies. Data processing trends indicate a shift toward integrating multiple monitoring methods. In the realm of non-contact remote sensing, technologies such as Terrestrial Laser Scanning (TLS), Unmanned Aerial Vehicles (UAVs) equipped with various sensors, and Interferometric Synthetic Aperture Radar (InSAR) are increasingly employed for subsidence monitoring. Laser scanning, particularly Mobile Laser Scanning (MLS), has gained popularity due to its high accuracy and ability to overcome limitations in data scanning range. More recently, smartphone-based LiDAR has gained prominence owing to its user-friendly nature and cost-effectiveness. Here we demonstrate both conventional and advanced measurement techniques, with a specific focus on smartphone LiDAR. While the reliability of smartphone LiDAR in geotechnical applications within underground mines is yet to be fully established, its advantages in terms of accessibility, usability, and integrated data processing are highlighted. The discussion also addresses inaccuracies stemming from smartphone positioning errors. Despite these challenges, smartphone-based LiDAR has the potential to be a useful technology for on-site data processing and real-time analysis. Future research can leverage these advantages to offer insights, preventive measures, and suggestions for further investigation.