Proceedings of the 5th International Conference on Transportation Geotechnics (ICTG) 2024, Volume 5

Reusing recycled waste materials are a major objective in transportation geotechnics for achieving a higher sustainability of earthworks and pavement activities in infrastructure construction and rehabilitation. This is the case with reclaimed asphalt pavement (RAP) that can be used as pavement base material. This paper aims to assess the deformation characteristics of compacted unbound granular mixtures containing natural limestone aggregates (70%) and RAP (30%). Cyclic load triaxial tests according to EN 13286-7 were carried out on granular mixtures compacted at different degrees of compaction (95% and 100%). Due to the viscoelastic behavior of RAP, sensitivity to the temperature of deformation characteristics was studied. Test specimens were conditioned and tested at different temperatures: 20, 30, and 40 °C. Tests were performed to assess permanent deformation and resilient behavior. In general, the results confirmed the influence of temperature on the deformation characteristics regarding the presence of RAP. However, the density had a more significant influence, especially in high temperatures.

Olive stone is a major solid by-product generated from olive oil mills. Due to its promising energy potential, olive stone is a suitable candidate for heat and electricity production via biomass gasification. Olive stone biochar (OSB) is the solid residue left after gasification. Typically, OSB is disposed of as a waste material in landfills. However, there is an opportunity to repurpose OSB as a sustainable geotechnical fill material. In this study, the engineering and environmental properties of OSB were thoroughly evaluated to assess the feasibility of using OSB in construction projects. Furthermore, recycled glass (RG), a mainstream waste material that has been successfully incorporated in civil engineering applications, was subjected to control tests for benchmarking purposes. Geotechnical tests, including particle size distribution, standard Proctor compaction, California Bearing Ratio, hydraulic conductivity, and repeated load triaxial, were conducted on both OSB and RG. The test results indicated that OSB can be satisfactorily used as a geotechnical fill material for pavement subgrade. Environmental test results, including pH, elemental analysis, and leachate analysis, indicated that the implementation of OSB in construction works does not pose negative environmental risks. Instead, the reuse of OSB in civil engineering applications can promote the circular economy of biomass waste, as not only olive stone can be used for energy generation, but also the residue after gasification has the potential to act as a useful construction material.

In Australia, domestic freight transportation has increased by around ten times during the past five decades and led to a significant upsurge in the construction and maintenance activities of railways. Therefore, it is important to consider upgrading the materials and techniques to address the growing requirements effectively. This study reviews the use of recycled-rubber inclusions including Recycled-Rubber Energy Absorbing Grids (REAG) derived from end-of-life rubber conveyor belts from the mining industry as a countermeasure to minimize track damage. A comparative review on the use of traditional polymer geogrids, Under Ballast Mats, and rubber grids in view of reducing track deformation and ballast breakage will be presented to assess the additional benefits of rubber, which include improved resiliency and damping properties in conjunction with interlocking granular particles.

In Australia, there has been a notable increase in the construction and maintenance of railways, and it is anticipated that these expenditures will continue to be substantial. This can be attributed to the significant expansion of urban and regional populations, the ongoing growth of trade activities, the environmental advantages associated with rail transportation compared to road transport, and an increasing need for maintenance services. Waste rubber derivatives applied in the ballasted railway substructure have shown improved energy-absorbing characteristics while satisfying engineering properties stated in railway specifications. The laboratory outcomes have been further investigated in an instrumented ballasted track stretch constructed near Sydney, Australia, by including innovative rubber derivatives within the track formation. This paper discusses the application of rubber intermixed ballast replacing the conventional ballast layer and assesses the performance of the modified track substructure compared to a conventional track. Onsite instrument data were utilized to analyse stress distribution, and vibrations in order to assess track performance.

The reuse and recycling of waste materials has become imperative as the construction industry strives to minimise its carbon footprint and contribute towards sustainable development. Taking into account that aggregates often represent the largest proportion of the materials used in railway foundations, the incorporation of alternative (i.e. recycled) aggregates could significantly reduce the adverse environmental impacts from the construction of such infrastructures. This paper discusses recent advances and challenges associated with the use of recycled C&D materials in the rail track substructure. A comprehensive laboratory study was carried out to assess the relevant physical, mechanical and chemical properties of different types of recycled C&D aggregates and to determine whether their application as alternative fill materials in the railway substructure would be feasible. Test results have shown that recycled aggregates from C&D waste may be suitable for inclusion in embankment and form layer of railway infrastructures. A major challenge related to the use of these recycled aggregates in the subballast layer is their relatively high susceptibility to breakage and wear. None of the recycled C&D materials raised any environmental concerns that could hamper their application in railway foundations.

This study aims to evaluate the suitability of cement-stabilized mixtures of recycled glass (RG), tire (RT), plastic (RP), and crushed recycled concrete aggregate (RCA), in pavement subbase applications. These blends were previously investigated and proved suitable as alternatives to crushed rock for backfilling deep excavated trenches in trafficable areas. This study explores their suitability under stress levels of pavement structural layers, which is important from a practical and material supply point of view. Specialized pavement and geotechnical testing was carried out on three proposed blends stabilized with 3% cement. The resilient modulus (Mr) characteristics were evaluated through the repeated load triaxial (RLT) test. To assess the material strength, the unconfined compressive strength (UCS) test was performed while the flexural strength and fatigue life of the blends were assessed using four-point flexural beam tests. The Mr, flexural stiffness, and fatigue life results were compared with the minimum requirements as recommended by the specifications for road subbase layers. The essential factors influencing the strength and resilient properties of the blends were the contents of RCA and RT. The Mr values for all proposed blends exceeded the minimum threshold required for a subbase layer. However, based on minimum flexural modulus required for subbase layer, one of the mixtures was recommended to be used as a potential alternative to the virgin quarry material.

Exploitation of traditional construction materials like natural crushed stones in road construction poses threats to the environment and its sustainability. On the other hand, increase in construction activities due to rapid industrialization and urbanization has come up with the generation of a large amount of demolition waste which ends up creating problems for the environment. Hence, the use of construction and demolition waste (CDW) as a recycled concrete aggregate in place of crushed stones in pavement construction can be considered as one of the promising methods to manage the CDW, and, at the same time, to protect the natural environment. In this regard, studies on the crushing characteristics of CDW becomes very important. The basic objective of the present study is to improve the crushing characteristics of CDW by mixing it with some suitable admixture. With this in view, one-dimensional compression tests were conducted by applying different stress levels to CDW mixed with different percentages of silica fume (i.e., 0, 5, 10, 15, and 20%) in the form of slurry to the CDW surface. The amount of crushing was calculated by using Hardin’s breakage factor, and the results were found to be very useful. Based upon the present study, the optimum percentage of silica fume can be 15%.

The granular layers of a conventional railway substructure, such as ballast and subballast or capping layer, are prone to particle breakage, and are comparatively more expensive than recycled waste materials in terms of capital and maintenance costs. Utilizing waste materials like mining waste such as steel furnace slag-coal wash (SFS + CW) mixtures and energy absorbing materials such as rubber crumbs (RC) for transportation infrastructure presents notable economic advantages, while being environmentally sustainable. Accordingly, prior investigations have examined the appropriateness of combining RC and SFS + CW as a viable alternative to conventional railway substructure materials, particularly in relation to the subballast layer. This paper presents the prediction of the behavior of steel furnace slag, coal wash, and rubber crumb (SFS + CW + RC) mixtures with a RC content of 20%, using the Nor-Sand model. The theoretical model is validated using static drained triaxial test data reported by Qi et al. (J Mater Civ Eng 30:018276, 2018).

Rapid urbanization have resulted in an increase in the demand for new housing, commercial buildings, and infrastructure projects. This may require getting rid of existing old structures leading to the generation of waste from construction and demolition (C&D) activities. The major part of the generated C&D wastes is typically dumped into landfills posing a severe threat to the environment. Recycled sand derived from C&D wastes can reduce the need for natural sand extracted from rivers beds, beaches, and other natural resources. In the present study, the viability of using recycled sand derived from a C&D waste recycling plant in the construction of road pavements is studied. The strength, deformation, and compaction characteristics of treated recycled sand are studied considering different cement contents (2, 4, and 6%). Based on the gain in the unconfined compressive strength of cement-treated recycled sand, broad guidelines to utilize treated recycled sand in low-volume road construction projects are proposed in the study.

The concept of green construction with recycled materials has been widely discussed and investigated lately. This paper introduces a sustainable option of a lightweight, porous, composite material with recycled waste glass (RWG) that can be used specifically for geotechnical applications such as columnar inclusions to support embankments for transport infrastructure constructed over soft ground. The material proposed here is a combination of RWG aggregates and RWG-based binder where the aggregate part is a coarse mix of poorly graded RWG ranging from 75 μm to 9.5 mm. An environmentally friendly binding mechanism with fine glass powder-based geopolymerisation is proposed here to substitute the traditional cement-based binders. General fine ground soda-lime glass powder (GP) was used as the precursor of the geopolymerisation, activated with 10 M sodium hydroxide and cured at 85 °C. Commercially available class F fly ash (FA) and cleaned waste aluminium foils (AF) were examined under two trials to evaluate the possibility of catering for the deficiency of aluminium in GP for a successful geopolymerisation process. AF pre-dissolved in sodium hydroxide in 2:1, Na:Al ratio proved to be the ideal filler of aluminium required for the geopolymerisation process. Further investigation on the above combinations showed that 24 h of curing at 85 °C results in the maximum compressive strength of the hardened composite mix. The mineralogical characterisation of the finalised binder mix with X-ray diffraction (XRD) and stagewise microstructure analysis with scanning electron microscopy (SEM) confirmed the geopolymerisation with the formation of an alkaline aluminosilicate (N–A–S–H) gel.

Cement is widely used in pavement construction. A cement-treated base (CTB) with increased strength, stiffness, and water resistance can not only provide good support for surface course but also reduce the in situ water content of soils improving cohesion between bituminous surface and base materials. However, cement production is typically associated with high greenhouse gas emissions and energy consumption. Coal char is a sustainable and eco-friendly byproduct and porous coal-derived material. Recent studies have shown that coal char can be used as a raw construction and building material to improve the engineering performance of cement based products. In this research, the feasibility of using coal char in CTB is evaluated. Coal char, produced from Powder River Basin coal in Wyoming was pyrolyzed at a temperature of 850 °C, resulting in a fixed carbon content of 80%. According to the mix design for CTB of Wyoming Department of Transportation (WYDOT), the total amount of cement in the mix is 1% by weight of material. The effect of different additives (1% cement, 1% char, 0.5% cement, and 1% char with respect to soil weight) on the properties of soils is investigated. Compared to cement-stabilized soils, the char–cement-stabilized soil with 50% less cement use exhibits significantly higher unconfined compressive strength (UCS) and Young’s modulus at 7 days and comparable UCS at 28 days. For uncemented soils, the addition of 1% char leads to 2.3% lower water content. The findings would be beneficial for achieving sustainable pavement construction.

Ballast, which serves as the primary foundation material for railways, undergoes deformation and deterioration due to the heavy, repetitive loads exerted by fast-moving trains. These effects pose safety and efficiency challenges for tracks, leading to increased maintenance needs. To address these issues, one promising approach involves using rubber mats (Under Sleeper Pads—USP and Under Ballast Mats—UBM) to stabilise ballasted tracks. These mats absorb energy, minimise particle breakage, enhance track stability, and improve safety and longevity. This paper examines the effectiveness of rubber elements in ballasted tracks based on extensive laboratory testing. The findings indicate that rubber mats dampen the deformation and degradation of ballast. Specifically, USPs are more effective in reducing vertical permanent deformation, while UBMs excel in reducing lateral deformation.

In the current circumstance of road construction, sustainability and social impact present significant challenges. Despite numerous pavement infrastructure projects, including new construction and rehabilitation, environmental impacts have escalated due to excessive consumption of natural aggregates and conventional Portland cement. This study aims to address these challenges by developing an alternative road material through the integration of sub-standard fine crushed rock (SFCR) and low carbon cement (LCC) into self-compacting concrete (SCC), promoting eco-friendliness. The research focused on incorporating SFCR, a by-product from a commercial rock quarry in Northern Thailand, into SCC. Particle size distribution (PSD) modification of SFCR facilitated waste management. Proportions of LCC and water in SCC mixes were systematically optimized, then evaluated their impact on fresh workability and unconfined compressive strength. Results showed that SCC mixes with coarser PSD exhibit higher strength and resilient modulus than finer mixtures. The selected SCC mixture demonstrated favorable flexural modulus and tensile fatigue resistance, surpassing traditional cement-treated natural gravel. Mechanical-empirical pavement design analysis and life cycle assessment (LCA) revealed that the chosen SCC mixture reduced total construction costs by approximately 7% and achieved over 30% savings in greenhouse gas emissions during road base construction. Eventually, this innovative material and concrete technique would align with sustainable development goals in civil engineering, offering a promising solution in waste management, and contributing to high eco-friendliness in infrastructure development industry.

In this present study, the effect of compaction temperature on the mechanical behavior of base material containing 100% RAP (Reclaimed Asphalt Pavement) with and without asphalt emulsion is analyzed by means of repeated triaxial tests, of the multistage type, to evaluate permanent deformation. The results demonstrated that RAP mixtures exhibit significant susceptibility to permanent deformation at all analyzed stages, and the addition of binder did not provide stabilization to the mixture; instead, it increased their susceptibility to deformation. Conversely, the temperature increases within the compaction range reduced the plastic deformations of RAP mixtures, making them more stable with behavior similar to, and even better than, the analyzed virgin crushed rock aggregate at lower stresses. Therefore, thermal compaction emerges as a viable alternative to mitigate the susceptibility to permanent deformation in the base layer composed of 100% RAP.

Due to rapid urbanization and improved construction activities in many developing countries and other metropolitan areas, the accumulation of demolition waste from construction demolitions in landfills is a worldwide issue. Demolition waste has a verse effect on the environment due to landfill and maintenance issues. The recycled sand employed in the study was obtained from a Construction and Demolition (C&D) processing plant situated in Hyderabad, India. Extensive physical and engineering characterization was performed on recycled sand. It is crucial to ascertain whether recycled sand can be utilized as a sustainable replacement for natural sand in order to ensure the efficiency and safety of constructions. The results show that the engineering characterization is high for recycled sand when compared with the test results for natural sand. The present study shows the technical suitability of recycled sand to use as backfill material in various engineering applications from a structural stability and performance point of view in reducing the demand for natural sand, which is often extracted from riverbeds and quarries. Using recycled sand in various engineering applications led to be an environmentally friendly and sustainable approach.

The construction industry contributes significantly to greenhouse gas emissions as a result of cement production, use of heavy machinery and consumption of large quantity of non-renewable resources. Additionally, the construction industry generates huge amounts of waste. The use of recycled aggregates in road pavements can significantly contribute to more sustainable infrastructures, minimizing the extraction of virgin aggregates and using secondary materials that would otherwise be discharged into the environment with negative impacts. In Portugal, as in most Southern European countries, most of recycled aggregates coming from Construction and Demolition (C&D) waste are mixed or non-selected recycled aggregates, containing concrete and mortars, aggregates, bituminous materials, masonries, among others. These materials are considered as low quality recycled aggregates, due to poor mechanical properties, namely their resistance to fragmentation and to wear, being their use in roadways pavement layers sometimes unfeasible. This paper presents results from a preliminary laboratory study carried out with different mixtures of a recycled aggregate with natural granitic aggregates and focused on the resistance to fragmentation. The behaviour of all the aggregates is also studied, analysing the resistance to fragmentation of different aggregate sizes or fractions. The results show that the performance of the recycled aggregate can be improved, but to comply with the requirements imposed by the Portuguese Road Infrastructures Management Entity, high percentages of natural aggregates with high fragmentation resistance are required.

Recycled concrete aggregates (RCA), derived from demolishing concrete buildings and pavements, have been treated with significant value as a recycled resource. Using RCA instead of virgin aggregates for pavement construction became a feasible approach to conserve construction trash resources since approximately 140 million tons per year were produced in the United States. This research conducted a life cycle cost analysis of stabilized clay subgrade soils in Kansas, USA, combining with RCA from pavements damaged by freeze-thaw cycles and the D-cracks process. Class C fly ash and type II Portland cement were stabilizers for subgrade mixture designs. The performance of the mixtures was evaluated through Standard Proctor, unconfined compression strength (UCS), and California Bearing Ratio (CBR) tests. The full-depth flexible pavements incorporating these stabilized subgrades were designed using the AASHTOWare Pavement ME Design (PME) software. Results indicated that a 1:1 mix of Class C fly ash and type II Portland cement was the most effective stabilizer, decreasing the required thickness of the hot-mix asphalt (HMA) layer. The life cycle cost analysis demonstrated that the RCA-stabilized subgrades are economically viable when the chemical stabilizers are used in equal proportions.

The Box Test apparatus plays a crucial role in simulating large-scale railway pavements, providing valuable insights into material performance under conditions closer to reality. This study utilizes the Box Test to comprehensively analyze the potential use of steel slag as a material for railway ballast, focusing on its characterization and evaluation of the resilient modulus for sustainable railway pavement viability. The research involved conducting various tests in accordance with Brazilian and American standards to assess the feasibility of steel slag as a ballast material. The results revealed that, while the slag meets certain regulatory limits, it exceeds specified limits for porosity and absorption. The study also assessed the elasticity modulus of the steel slag ballast, confirming its positive outlook and contribution to the feasibility of sustainable railway pavement. The article emphasizes the significance of large-scale experiments in simulating railway pavements, providing valuable insights into the potential of steel slags as ballast material. The research is ongoing, with the completion of full-scale tests to fully simulate the pavement and observe layer interactions under more representative conditions. It is anticipated that the Box Test experiments results will provide a more comprehensive understanding of material performance in realistic conditions, contributing to a better understanding of railway pavement and offering insights into the feasibility of steel slags for the desired applications.

The influence of cyclic loading on the deformation response of granular materials is usually described using the shakedown concept. The shakedown response can be characterized into different shakedown regions such as plastic shakedown, plastic creep and incremental collapse regions depending on the incremental plastic strains that occur in each loading cycle. Though different incremental strain limits are proposed in literature for different granular materials, the boundaries between these three stages in terms of stresses are still unclear. In this paper, the influence of loading conditions such as loading magnitude, frequency of loading, confining stress etc. and material compositions such as rubber content on the shakedown behavior of different granular mixtures is investigated. It is found that the normalized cyclic stress ratio which is a ratio of the cyclic stress amplitude to material’s peak strength under static loading conditions can be used as a threshold value separating the plastic shakedown stage and plastic creep stages. By looking at laboratory data on two different granular materials, a unified criterion for estimating the shakedown limit under a wide range of loading and mixture properties is presented.

Unpaved forest roads are commonly used to provide access to forest areas for the operations associated with the exploitation of their products, to prevent and fight forest fires and for leisure activities. The forest value chain incorporates a multitude of diverse industries that generate a range of byproducts as part of their activities. One of these byproducts are fluidized bed sands, produced in the biomass boilers used for energy generation at pulp and paper plants. Heretofore, these byproducts were rejected like a waste and stored in waste landfills. Currently, efforts are ongoing to reuse the fluidized bed sands in unpaved forest roads. This approach promotes circular economy and the use of these byproducts as a valuable resource. Initial findings relating to the potential use of fluidized bed sands for unpaved roads are presented. In particular, geotechnical and chemical properties of these sands are evaluated and compared with the requirements for application as aggregate or infill soil on unpaved roads. The chemical and geotechnical properties of the byproducts tested fulfil the requirements of several guidelines. Therefore, these byproducts have potential to be used to replace natural materials in unpaved forest roads without negative environmental impacts.

The utilisation of waste is a key approach to moving towards a sustainable environment. A lot of research is going on about different waste materials to make them reusable for various activities in the construction industry. Recycled concrete aggregate is one of the industrial wastes that can be used as a base and sub-base course material in the construction of roads. Previous studies explored various aspects of its performance to minimise the use of natural aggregates. In this study, experimental results of consolidated drained triaxial tests of recycled concrete aggregate are simulated on PLAXIS 2D software considering the Hardening soil model with small strain and NorSand model. The experiments are conducted under 40, 70, and 100 kPa cell pressure. The comparison between experimental and numerical data of recycled concrete aggregate indicated that the NorSand model works better than the hardening soil model in terms of capturing stress–strain with post-peak softening behaviour.

In Australia, most rail systems are constructed along the coastal line, traversing soft soil deposits that can cause a series of track instabilities, including excessive plastic deformation and mud pumping. For this reason, the subgrade is considered one of the most critical components of the railway infrastructure, and the accurate prediction of its undrained shear behaviour is of utmost importance to ensure track integrity and safety over time. The subgrade is composed of naturally deposited soil, which may be modified using compaction or consolidation techniques to improve its bearing capacity. In each method, the soil presents a unique arrangement of particles, groups of particles, and voids (referred to as fabric), which govern the response of subgrade soils to the substantial loads imposed by moving trains. For this study, samples of clayey subgrade soil were collected from a site where track degradation had been reported. The soil was reconstituted using slurry consolidation and compaction methods to create different fabrics. A series of undrained cyclic triaxial tests were then carried out to investigate the influence of specimen preparation methods on the shear behaviour of soil. Differences in soil fabric were assessed through X-ray microcomputer-tomography (micro-CT), providing insights into the variations observed in the cyclic response. Based on the findings, it is evident that fabric plays a crucial role in the shear behaviour of subgrade soils and should, therefore, be considered in railway infrastructure design.

Railway subgrades are always subjected to cyclic loading with intermittent rest periods. When railways are built on low permeable soft estuarine clays, excess porewater pressures (EPWP) can accumulate and reach critical levels under prolonged loading conditions. Although numerous studies have been conducted on the clay subgrade under continuous cyclic loading, the behaviour during the rest period has not been studied to a greater extent. Large-scale cyclic consolidation tests conducted in the laboratory, considering two-way drainage, suggest that accumulated EPWP during cyclic loading redistributes during the rest period. Therefore, when adequate rest periods with proper drainage are present, the occurrence of EPWP reaching critical levels can be avoided. This paper presents an analytical model that can predict EPWP accumulation and dissipation. The proposed model is validated using the results of large-scale cyclic consolidation tests.

Fluidisation in saturated subgrades of transport infrastructure is a huge problem in many countries around the world caused by dynamic cyclic loads due to heavy haul trains on railways and heavy trucks on highways. The mechanism of subgrade fluidisation has been experimentally studied to a significant extent. However, numerical studies that have been carried out for studying fluidisation are limited. The first part of the paper includes a critical review of previous studies on the mechanism and the effect of cyclic loading factors on fluidisation. It is vital to conduct a comprehensive study with numerical modelling to simulate the actual field conditions of transport infrastructure to find reliable and cost-effective solutions to mitigate subgrade fluidisation. This goal can be achieved only by choosing a soil constitutive model that can capture the changes to the soil stiffness and strength due to excess pore pressure generation and dissipation, along with accumulated deformations in clay soil subjected to cyclic loading. Therefore, in this study, the SANICLAY constitutive model is selected as the suitable candidate to fulfil those requirements. It is implemented in the ABAQUS/Standard finite element program using the user-developed material subroutine UMAT. In the second part of the paper, the validation of the SANICLAY model that accounts for the anisotropy and structure of natural clay was presented using triaxial test data found in the literature for undisturbed clay. Application of the model to simulate cyclic loading shows that the version of SANICLAY used in the simulations needs modifications to capture the stiffness and strength degradation during cyclic loading.

Long-term traffic loadings will induce strong vibrations in the saturated ground, and it probably produces excessive settlements of saturated ground and even various distresses (such as cracks and leakage) of the tunnel structure. To better understand the long-term cyclic deformation behaviors of saturated clay subjected to cyclic traffic loading, a series of cyclic undrained hollow cylinder apparatus tests were performed on Shanghai saturated clay. The secondary cyclic compression stage of permanent axial strain, energy dissipation, and damping ratio are employed to identify the distinct shakedown ranges of saturated clay. Moreover, attempts are made to establish a link between the permanent deformation behavior invoked by different levels of dynamic stress and a kinematic yielding framework. The cyclic test results of Shanghai clay can be classified as plastic shakedown, plastic creep, and incremental collapse, and Y2 and Y3 yield limits are interpreted as threshold cyclic dynamic stress to divide the shakedown ranges. Additionally, the effective cyclic dynamic stress ratio can better identify the shakedown ranges of saturated clay. Eventually, a criterion is recommended to identify distinct shakedown ranges of saturated clay. The findings will contribute to the safe design of the transport infrastructure in saturated ground.

Natural soft soils beneath transportation infrastructures sustain typical structured properties and are characterized by high sensitivity and poor engineering performance, which pose great challenges for the efficient operation of high-speed trains. Under traffic loading, soft subsoils present shakedown response and accumulate no negligible deformation. While few constitutive models are available both for the long-term behavior description of soft soils under cyclic loading and structure degradation of soil. Herein, a conceptual constitutive model within bounding surface theory framework was established to depict the dynamic behavior of soft clay under high-cycle, low-amplitude loading. The bounding surface could expand due to the hardening effect caused by contractive plastic deformation, and it could simultaneously shrink due to the weakening effect caused by both soil destructuration and excess pore water pressure. To further validate the proposed model, relevant triaxial tests were referenced. The consistent plastic deviatoric strain and excess pore water pressure from tests and the prediction confirmed the effectiveness of the proposed model. Following a comprehensive analysis of the varying internal variables during cyclic loading and a thorough investigation into the damage effects related to plastic strains, the model was considered capable of reasonably describing the structure destruction of soft soil to long-term cyclic load.

This paper addresses the cyclic behaviour and stiffness degradation of subgrade soils subjected to stress-controlled cyclic loading, with particular emphasis on soils that are prone to mud pumping or subgrade instability. With continuous passage of trains over weak, saturated, low-plastic subgrade foundations, the finer fraction of the soils tends to fluidise (i.e., behave like a fluid) and migrate upwards, thereby, fouling the ballast and hindering the long-term performance of the rail track infrastructure. This leads to significant costs associated with annual track maintenance. Through a series of undrained cyclic triaxial testing varying the cyclic stress ratio (CSR, representing the axle loads) and loading frequency (simulating train speeds), the authors noted a significant upward migration of finer fraction coupled with internal moisture redistribution within the failed specimens. Further analysis revealed the instability of specimens was caused by early softening behaviour, and it is accompanied by a sharp reduction in the specimen stiffness. To tackle this, the stiffness was evaluated in terms of axial dynamic modulus and strain energy per cycle was evaluated to better understand the fluidisation behaviour. A novel quasi-linear relationship between threshold residual strain and number of cycles is proposed to serve as a practical guide.

Transport infrastructure is linear and often intersects and is comprised of (i.e. geostructures) several soils of differing characteristics i.e. particle size, mineralogy and thus plasticity. Evaluation of these properties, for example by monitoring small strain stiffness, is critical for assessing compacted soil geomechanical behaviour during service. In this paper the influence of drying-wetting is investigated for three compacted soils representative of soils in the UK, including a low plasticity clayey sandy silt, a high plasticity kaolin clay, and a very high plasticity silty clay. The impact of their composition (e.g. clay content and plasticity) on shear wave velocity during a drying-wetting cycle was monitored at selected gravimetric water content levels. As expected, the results show that higher clay activity (A) results in larger variation of shear wave velocity. In addition, soils with a higher Weighted Plastic Index (WPI) also exhibit larger volumetric changes during drying-wetting. Consequently, the results quantitatively capture the influence of the clay content, which shows a significant effect on the variation in seasonal geomechanical performance. These findings can in turn support proactive asset management strategies that enable the identification of areas of the transport network that may be more vulnerable to seasonal changes in water content.

The use of biochar in earthwork and slope engineering has gained significant interest due to its water and nutrition retention capacity that gives buffer against extreme wetting and drying, as well as helping vegetation growth. Recently, biochar-mixed soil has been proposed as an alternative cover material for embankments and cut slopes for roads in tropic regions. Designing the hydraulic barriers with biochar-mixed soil in earthwork systems needs clarification of water infiltration behavior into the soil. However, the physical and hydro-mechanical properties needed for application and assessment of hydraulic barrier by biochar-mixed soil are not yet fully understood. In this study, the impacts of biochar amount and types of biochar used on the hydraulic and mechanical characteristics of biochar-mixed compacted clayey sand were investigated by testing two different biochars deriving from rice husk and woodchip. The soil compaction test, permeability test, soil water characteristic tests and numerical study for seepage analysis were conducted for studying the biochar-mixed soil compared with mother soil. The microscopy and mercury intrusion porosimetry provided pore size distribution of biochars to deepen the understanding of mechanisms of water retention in biochar-mixed soils. The results showed that biochar addition increases the micropore which is expected to have higher water capacity, owing to the porous nature of the biochars. It is also shown that the biochar-mixed layer could delay water infiltration when biochar amount addition is large and sufficient. With the same biochar content, rice husk can help to reduce water infiltration more than woodchip.

Compacted clay is extensively used as foundation materials, generally presenting unsaturated state. Understanding the soil arching effect in unsaturated compacted clay under unloading is meaningful for ensuring its performance, but nowadays still limited. A series of two-dimensional trapdoor model tests were conducted to investigate the stress redistribution and deformation mechanism caused by the soil arching effect in unsaturated compacted clay under unloading. Different initial placement conditions (dry densities and water contents) of clay were considered. From the results of the trapdoor tests, the effect of the initial placement condition of the soil is significant for the characteristics of the soil arching effect in unsaturated compacted clay, including the deformation development and the stress redistribution. The results can provide a technical reference for estimating and fully using the soil arching effect in unsaturated compacted clay during geotechnical design.

The promoted advantages of implementing stiffness-based compaction specifications include that they enhance the efficiency and accuracy of compaction practices in earthworks projects, as they have the potential to improve project outcomes and cost-effectiveness. But reliably achieving the traditionally desired compaction targets, such as dry density, through correlation with stiffness indexes has remained a challenge for earthworks practitioners. In this study, we investigate two stiffness and compaction field trials. The presented results include in-situ stiffness parameters that can be easily determined during the production phase of earthworks Compaction Measurement Value (CMV) and Light Weight Falling Deflectometer (LWD)—and typical compaction assessment data from nuclear density gauge, plate load test, and particle size analysis. A novel empirical framework that links stiffness to density and degree of saturation is applied to the datasets. The analysis of the field trials encompasses an evaluation of the successes and challenges encountered in each case and discusses the potential areas of improvement for future trials and the potential for the creation of stiffness-based compaction specifications.

The conventional disposal of construction and demolition (C&D) waste increases the burden of landfills. Recycling and reusing can be an environmentally friendly and economically affordable means for the management of C&D waste. This paper investigated the performance of aggregate with different mixture percentages of recycled concrete aggregate (RCA) and natural aggregate (NA) with diverse fine contents as road base materials. The compaction behaviour, California bearing ratio (CBR), and resilient modulus were determined. The results indicated that the mixture containing 50% RCA had the highest CBR values and resilient modulus. This suggested CBR and resilient properties of NA can be improved by the incorporation of RCA.

Soil serves as a primary construction material for roads. Chemical properties of soil, including acidity, and salinity, have the potential to erode concrete, steel structures, road furnishings, and cause land degradation in a vicinity of roads. Acid sulphate soils (ASS) are naturally found in soil sediments and contain iron sulfides, primarily in the form of pyrite. Such soils are typically located in low-lying coastal areas of Australia. Under anerobic conditions, acid sulfate soils do not pose a significant environmental risk. However, when these soils are disturbed by construction activities such as excavation, and temporary or permanent dewatering there is a possibility for the iron sulfides present in the soil to react with oxygen, leading to the generation of sulfuric acid. This acidification process can affect the landscape by lowering its pH and results in releasing of contaminants, including iron, aluminum, and other metals in harmful concentrations. These contaminants have the potential to be transported to waterways, wetlands, and groundwater. Contrary to alkaline soils, acidic soils pose a significant risk to infrastructure, particularly steel or metallic structures. There is a risk of sustained damage to infrastructure over time due to the corrosive effects of acidic water on metallic and concrete structures. Presence of acidic soil can cause decay or absence of roadside vegetation resulting in accelerated soil erosion, leading to substantial and lasting damage to the road structure.

To investigate the influences of water saturation on dynamic responses in the unsaturated ground under moving load, this study derives Biot form governing equations for a three-phase unsaturated medium that can be easily solved using the solution framework of a single-phase or double-phase medium. The governing equations are solved via two-and-half dimensional finite element method (2.5D FE method). A 2.5D FE model of embankment-unsaturated ground system with the consideration of node’s 9 DOFs (degree of freedoms) is established. Through the numerical analysis, it is found that when the load speed is during 0.5 $${V}_{C}^{min}$$ V C min to $${V}_{C}^{min}$$ V C min ( $${V}_{C}^{min}$$ V C min is critical velocity of 100% saturated soil), the displacement responses at the embankment surface are independent of the load speed and only determined by the product of load speed and water saturation cSr. When the load speed $$<$$ < 0.5 $${V}_{C}^{min}$$ V C min , the displacement response amplitudes are independent of the load speed, mainly determined by the water saturation.

Soil-rock mixture is a commonly used subgrade filling material in high-fill transportation engineering with heterogeneous compositions and complicated mesostructure. A novel degradation model for rock blocks is established based on the Discrete Element Method to capture the compressive behaviors of soil-rock mixtures. The gradual degradation process of rock blocks can be considered, including slight degradation, corner breakage, and fracture. Among them, the simulation method of slight degradation is proposed based on the idea of contact detach, and can reflect the nonlinear stiffness between rock block particles. The simulation of corner breakage adopts a method that considers the size effects and the Weibull distribution of rock strength. And the simulation method for fracture or smash is to search for rock blocks bearing excessive stress and replacing them with breakable clusters. The DEM model was calibrated with the laboratory test result of force–displacement curve in particle compression test. Then, a series of large-scale confining compression test simulations have been carried out to analyze the compression deformation behaviors and particle contact characteristics with different vertical stress and rock block proportion. The results show that for the selected sample, the stiffness is relatively high when the rock content is between 50 and 80%, which can be well explained from a meso-scale perspective.

In recent years, railway embankments often collapsed due to severe rainfall in Japan. It is well known that the stability of the embankments decreases if the water level or the degree of saturation increases after rainfall. However, the characteristics of the accumulated settlement after the occurrence of severe rainfall has not been studied clearly. In this study, the cyclic triaxial tests using existing embankment materials were performed to study the influence of the kind of materials or the loading conditions on the characteristics of accumulated settlement. Furthermore, the influence of the change of the water content during cyclic loading was studied in order to evaluate the influence of rainfall on the characteristic of the accumulated strain.

Frost heave is always observed in unsaturated coarse-grained soil subgrades of high-speed railways in cold and arid regions. However, these subgrades have very low water contents and are located above the groundwater table. Vapour transfer induces frost heave in unsaturated soils has attracted much attention. However, there is little direct evidence. In the present research, we conducted field monitoring of subgrade in cold regions. The results indicated that frost heave can occur in the unsaturated coarse-grained soil subgrade with a fine content of less than 5% in the absence of groundwater supply. The maximum frost heave is approximately 8 mm, and the frost depth is about 1 ~ 1.5 m. Moreover, the one-dimensional frost heave experiments on coarse-grained soil with vapour supply were conducted. The results demonstrated that the transfer and supply of vapour could increase the water content in the soil and induce frost heave. It also proved that vapour transfer could induce the frost heave in unsaturated coarse-grained soil subgrades in cold and arid regions.

Understanding the soil’s water retention characteristics is crucial to monitoring and managing the earthwork infrastructures, especially during wetting induced by extreme rainfall. The adsorption of water (hydraulic wetting) and compression (mechanical wetting) of the soil skeleton can result in a higher degree of saturation (Sr). This study investigated the water retention characteristics of sandy loam wetted by two different wetting methods. Data were obtained from a one-dimensional compression apparatus for unsaturated soil. Stress-controlled and suction-controlled tests were conducted. The degree of saturation (Sr), matric suction (s), and void ratio (e) were simultaneously measured. The soil water retention curves (SWRCs), compressibility, and the e-s-Sr relationship were analysed. Finally, a typical physical model of e-s-Sr was employed to fit and analyse measured data. The results indicate that the void ratio is essential in determining the soil’s water retention curves. Denser soil performs better water retention capability. Due to suction-induced softening, the yield stress significantly decreases with lower matric suction. During the suction-controlled compression tests, the Sr slightly increases but is limited by the soil’s compressibility. The fitting results of Hu’s model indicated the dependence of the SWRC on the wetting method. It is necessary to consider the wetting paths in hydromechanical modelling for unsaturated soils.