The reasonable value of good gradation characteristic parameters is key in designing and optimising soil-rock mixed high fill embankment materials. Firstly, the DJSZ-150 dynamic-static large-scale triaxial testing instrument was used for triaxial compression shear tests on compacted skeleton structure soil-rock mixture standard specimens. The changes in strength and deformation indicators under different gradation parameters and confining pressure were analysed. Then, based on the Janbu empirical formula, relationships between parameters K, n, and (sigma 1-sigma 3)ult and the coefficient of uniformity Cu and coefficient of curvature Cc were explored. Empirical fitting formulas for Duncan-Chang model constants a and b were proposed, establishing an improved Duncan-Chang model for soil-rock mixtures considering gradation characteristics and stress states. Finally, based on significant differences in particle spatial distribution caused by gradation changes, three generalised models of matrix-block stone motion from different particle aggregation forms were proposed. Results indicate the standard specimen's strength and deformation indicators exhibit significant gradation effects and stress-state correlations. The improved Duncan-Chang model effectively simulates the stress-strain relationship curve under different gradations and confining pressure, with its characteristics explainable based on the matrix block stone motion generalised model.

A comprehensive series of tests, including dynamic triaxial, monotonic triaxial and unconfined compressive strength (UCS) tests, were carried out on reconstituted landfill waste material buried for over twenty years in a closed landfill site in Sydney, Australia. Waste materials collected from the landfill site were treated with varying percentages of cement, and both treated and untreated specimens were investigated to evaluate the influence of cement treatment. The study examined the dynamic properties of cement-treated landfill waste, including cumulative plastic deformation, resilient modulus, and damping ratio, and also analysed the impact of cyclic loading on post-cyclic shear strength in comparison to pre-cyclic shear strength. The UCS tests and monotonic triaxial tests demonstrated that untreated specimens subjected to monotonic loading exhibited a progressive increase in strength with rising axial strain, whereas cement-treated specimens reached a peak strength before experiencing a decline. During cyclic loading, with the inclusion of cement, a significant reduction in cumulative plastic deformation and damping ratio was observed, and this reduction was further enhanced with increasing cement content. Conversely, the resilient modulus showed substantial improvement with the addition of cement, and this enhancement was further amplified with increasing cement content. The formation of cementation bonds between particles curtails particle movement within the landfill waste material matrix and prevents interparticle sliding during cyclic loading, leading to lower plastic strains and damping ratio while increasing resilient modulus. Post-cyclic monotonic testing revealed that cyclic loading caused the partial breakage of the cementation bonds, resulting in reduced shear strength. This reduction was higher on samples treated with lower cement content. Overall, the findings of the research offer crucial insights into the possibility of cement-treated landfill waste as a railway subgrade, laying the groundwork for informed design decisions in developing transport infrastructure over closed landfill sites while using landfill waste materials available on site.

The influence of seismic history on the liquefaction resistance of saturated sand is a complex process that remains incompletely understood. Large earthquakes often consist of foreshocks, mainshocks, and aftershocks with varying magnitudes and irregular time intervals. In this context, sandy soils undergo two interdependent processes: (i) partial excess pore water pressure (EPWP) generation during foreshocks or moderate mainshocks, where seismic loadings elevate EPWP without causing full liquefaction and (ii) incomplete EPWP dissipation between seismic events due to restricted drainage. These processes leave behind persistent residual EPWP, reducing the liquefaction resistance during subsequent shaking. A series of cyclic triaxial tests simulating these mechanisms revealed that liquefaction resistance increases when the EPWP ratio r(u) < 0.6-0.8 (peaking at r(u) similar to 0.4) but decreases sharply at higher r(u). Crucially, EPWP generation during seismic loading plays a dominant role in resistance evolution compared to reconsolidation effects. Threshold lines (TLs) mapping r(u), the reconsolidation ratio (RR), and peak resistance interval (the range of r(u) where the peak liquefaction resistance is located) indicates that resistance decreases above TLs and increases below them, with higher cyclic stress ratios (CSR) weakening these effects. These findings provide a unified framework for assessing liquefaction risks under realistic multi-stage seismic scenarios.

Subway subgrades typically consist of alternating deposits of soil layers with significantly different physical and mechanical properties. However, the overall dynamic characteristics and the evolution of micro-porous structures in stratified soils is often overlooked in current studies. In this study, cyclic triaxial tests were conducted on homogeneous sand, silt and stratified soils with different height ratios, and nuclear magnetic resonance (NMR) was used to investigate the changes in pore structure and moisture content. The dynamic behavior and macroscopic deformation mechanisms were systematically investigated in terms of stress amplitude, confining pressure, and layer height ratio (the ratio of sand to silt height). The results show that as the sand height ratio increases, the axial strain and pore water pressure first increase and then decrease, reaching the maximum when h(Sand): h(Silt) = 2:1. When the confining pressure is 100 kPa, the axial strain of h(Sand): h(Silt) = 2:1 is 181.08 % higher than that of silt. Under the dynamic loading, the stratified soils form a dense skeletal structure near the stratification plane, which hinders the flow and dissipation of pore water, so that the pore water agglomeration phenomenon occurs near the stratification plane, which aggravates the accumulation of residual pore pressure and reduces the deformation resistance. However, when h(Sand): h(Silt) = 4:1, the influence of the stratification planes is significantly reduced, and the deformation characteristics approach homogeneity. This study reveals the dynamic characteristics of stratified soils by comparing and analysing homogeneous samples.

In cold regions, the strength and deformation characteristics of frozen soil change over time, displaying different mechanical properties than those of conventional soils. This often results in issues such as ground settlement and deformation. To analyze the rheological characteristics of frozen soil in cold regions, this study conducted triaxial creep tests under various creep deviatoric stresses and established a corresponding Discrete Element Method (DEM) model to examine the micromechanical properties during the creep process of frozen clay. Additionally, the Burgers creep constitutive model was used to theoretically validate the creep deformation test curves. The research findings indicated that frozen clay primarily exhibited attenuated creep behavior. Under low confining pressure and relatively high creep deviatoric stress, non-attenuated creep was more likely to occur. The theoretical model demonstrated good fitting performance, indicating that the Burgers model could effectively describe and predict the creep deformation characteristics of frozen clay. Through discrete element numerical simulations, it was observed that with the increase in axial displacement, particle displacement mainly occurs at both ends of the specimen. Additionally, with the increase in creep deviatoric stress, the specimen exhibits different deformation characteristics, transitioning from volumetric contraction to expansion. At the same time, the vertical contact force chains gradually increase, the trend of particle sliding becomes more pronounced, and internal damage in the specimen progresses from the ends toward the middle.

It is generally believed that loess is not prone to liquefaction. However, on December 18, 2023, a magnitude 6.2 earthquake occurred in Gansu Province, China (35.70 degrees N, 102.79 degrees E), triggering a large-scale loess liquefactioninduced flow slide spanning 2.5 km, approximately 10 km from the epicenter. To understand the disastercausing mechanism, this study obtained the physical and mechanical properties of loess in the source area through field surveys and laboratory tests, and characterized the liquefaction behavior of saturated loess layers. The findings indicate that the strong ground motion, saturated loess, and gentle slope collectively contribute to the prevailing dynamic, geological, and topographic conditions. The saturated loess layer primarily comprises silt particles with particle sizes less than 0.075 mm accounting for approximately 92.2 % of its composition. The saturated loess layer at a depth of 11m was liquefied under the action of seismic waves with a peak ground acceleration of 0.40 g, however, due to the unique pore structure of loess, it is observed that pore pressure development rate lags behind strain rise rate during liquefaction process. The majority of strain accumulation occurred during a distinct post-peak stabilization phase following peak seismic activity while pore pressure continues to escalate even after vibration ceases. The results provide scientific insights into understanding the cause contributing to loess liquefaction induced-flow slide disasters due to earthquake.

Mastering the mechanical properties of frozen soil under complex stress states in cold regions and establishing accurate constitutive models to predict the nonlinear stress-strain relationship of the soil under multi-factor coupling are key to ensuring the stability and safety of engineering projects. In this study, true triaxial tests were conducted on roadbed peat soil in seasonally frozen regions under different temperatures, confining pressures, and b-values. Based on analysis of the deviatoric stress-major principal strain curve, the variation patterns of the intermediate principal stress, volumetric strain and minor principal strain deformation characteristics, and anisotropy of deformation, as well as verification of the failure point strength criterion, an intelligent constitutive model that describes the soil's stress-strain behavior was established using the Transformer network, integrated with prior information, and the robustness and generalization ability of the model were evaluated. The results indicate that the deviatoric stress is positively correlated with the confining pressure and the b-value, and it is negatively correlated with the freezing temperature. The variation in the intermediate principal stress exhibits a significant nonlinear growth characteristic. The soil exhibits expansion deformation in the direction of the minor principal stress, and the volumetric strain exhibits shear shrinkage. The anisotropy of the specimen induced by stress is negatively correlated with temperature and positively correlated with the bvalue. Three strength criteria were used to validate the failure point of the sample, and it was found that the spatially mobilized plane strength criterion is the most suitable for describing the failure behavior of frozen peat soil. A path-dependent physics-informed Transformer model that considers the physical constraints and stress paths was established. This model can effectively predict the stress-strain characteristics of soil under different working conditions. The prediction correlation of the model under the Markov chain Monte Carlo strategy was used as an evaluation metric for the original model's robustness, and the analysis results demonstrate that the improved model has good robustness. The validation dataset was input to the trained model, and it was found that the model still exhibits a good prediction accuracy, demonstrating its strong generalization ability. The research results provide a deeper understanding of the mechanical properties of frozen peat soil under true triaxial stress states, and the established intelligent constitutive model provides theoretical support for preventing engineering disasters and for early disaster warning.

Soybean urease-induced calcium carbonate precipitation (SICP) is an innovative and eco-friendly approach with demonstrated potential for mitigating soil liquefaction. However, the specific impacts of the concentrations of soybean urease and salt solutions require further elucidation. The research examines how the two compositions influence calcium carbonate formation. Dynamic characteristics of one-cycle SICP-treated clean and silty sand were analyzed based on cyclic triaxial tests. It was revealed that SICP-treated specimens of both liquefied sand and silty sand exhibit reduced accumulation of excess pore pressure and diminished strain growth under cyclic loading, thereby delaying liquefaction failure. Although higher concentrations of both soybean urease and salt solution can enhance liquefaction resistance, salt solution concentration has a more pronounced effect on improving liquefaction resistance due to the more production of calcium carbonate. Scanning electron microscopy observations confirmed the presence of calcium carbonate crystals at the interfaces between sand particles and between sand and fine particles. These crystals effectively bond the loose sand and fine particles into a cohesive matrix, reinforcing soil structure. A direct linear correlation was established between the liquefaction resistance improvement and precipitated calcium carbonate content. Notably, the one-cycle SICP treatment method adopted in this study demonstrates a better biocementation effect compared to cement mortar or multi-cycle MICP-treated sand under the same content of cementitious materials. These findings provide valuable insights for optimizing SICP treatments, aiming to reduce the risk of soil liquefaction in potential field applications.

Granular materials usually copossess inherent and stress-induced anisotropy that significantly influences their mechanical behaviors. This paper presents a series of true-triaxial tests on aeolian sands to consider the inherent and stress-induced anisotropy in terms of soil deposition angles and intermediate principal stress coefficients, respectively. These results show that the deposition angle primarily affected the elastic-plastic stage under axisymmetric conditions. Otherwise, the deposition angle affects all deformation processes after the elastic stage when the intermediate principal stress coefficient changes. Moreover, the critical state is not unique but depends on the combined effect of the deposition angle and the intermediate principal stress coefficient, which indicates that the strength, stress-strain response, and dilatancy behavior of sands are affected by both inherent and stress-induced anisotropy.

Discrete element modeling (DEM) is a useful tool for linking global responses of granular materials to underlying particle-level interactions. A DEM model capable of capturing realistic soil behavior must be calibrated to a reference dataset, typically consisting of laboratory experiments. Calibration of a DEM model often requires numerous simulations as contact parameters need to be iterated upon until the simulation results satisfactorily replicate the experimentally observed behaviors. This paper presents a sensitivity investigation that examines the effects of the contact parameters on the drained triaxial compression response of a poorly-graded sand. It then introduces a calibration procedure capable of providing contact parameters that satisfactorily reproduce the results of laboratory triaxial results in a few simulations. Results show that friction and rolling resistance coefficients jointly influence the mobilized peak and critical state friction angles, secant shear modulus, maximum dilation rate, total volumetric strain, and strain softening magnitude. These parameters also influence the mode of failure at contacts and the evolution of fabric anisotropy. The influence of mu r or mu on the triaxial response and particle-level interactions is coupled, becoming more profound as the other parameter is increased. Contact stiffness is shown to influence the shear modulus and volumetric change behavior independently of mu and mu r. An algorithm that estimates values for mu and mu r needed to reproduce experimental results is developed using triaxial response parameters from experimental datasets. The performance of the proposed calibration method is demonstrated for three natural sands showing that it provides appropriate calibrated parameters for poorly graded sands with different relative densities and confined with varying effective stress magnitudes.