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.

The physical and mechanical characteristics of saline soil are significantly influenced by salt content, with macro- and mesoscopic mechanical properties closely correlated. This study investigates the strength and deformation behaviors of saturated saline sand through indoor triaxial shear testing under varying confining pressures and salt contents. The key innovation lies in developing a coupled finite element and discrete element analysis model to simulate the mesoscopic behavior of saline sand under triaxial shear stress state. Flexible boundary conditions were applied, and appropriate contact models for salt-sand interactions were selected. By adjusting mesoscopic parameters, stress-strain curves and variations in porosity, coordination number, particle displacement, and contact force chains were analyzed. The study further explores shear band development and shear failure mechanisms by examining relative particle displacement and the breaking of contact force chains. Additionally, the influence of salt particle size on the overall strength of the DEM model was assessed. The findings provide valuable insights into the internal structural changes of saline sand during shear deformation, contributing to a better understanding of its mechanical behavior in engineering applications.

Recently, the biostimulation has received attention due to its sustained mineralization, environmental adaptability and lower cost. In the current study, a series of isotropic consolidated undrained triaxial shear (CU) tests were performed on biocemented soil treated through biostimulation approach to examine the effect of cementation levels on the undrained shear behaviors. The test results demonstrate that the biocementation generated by the biostimulation approach can improve the shear behaviors remarkably, with the observed changes in stress-strain relationship, pore water pressure, stress path, stiffness development, and strength parameters. The variations of the strength parameters, i.e., effective cohesion and effective critical state friction angle, with increasing cementation treatment cycles can be well fitted by an exponential function and a linear function, respectively, while the variation of the effective peak-state friction angle is relatively small. The increased shear strength, stiffness, effective cohesion, and strain softening phenomenon of biocemented soils are related to the densification, increased particle surface roughness, and raised interparticle bonding caused by biostimulation approach. The liquefaction index decreases with the increase in cementation treatment cycles, especially at lower initial mean effective stress (100 and 200 kPa), indicating that the biostimulation approach may be a viable method for anti-liquefaction of soil.

To investigate the mechanical response characteristics of damming rockfill materials under different confining pressure conditions, this study integrates laboratory triaxial compression tests and PFC2D numerical simulations to systematically analyze their deformation evolution and failure mechanisms from both macroscopic and microscopic perspectives. Laboratory triaxial test results demonstrate that as the confining pressure increases, the peak deviatoric stress rises significantly, with the shear strength of specimens increasing from 769.43 kPa to 2140.98 kPa. Under low confining pressure, rockfill exhibits pronounced dilative behavior, whereas at high confining pressure, it transitions to contractive behavior. Additionally, particle breakage intensifies with increasing confinement, with the breakage rate rising from 4.25% to 8.33%. This particle fragmentation alters the granular skeleton structure, thereby affecting the overall mechanical properties and leading to a reduction in shear strength. Numerical simulations further reveal the micromechanical mechanisms governing rockfill behavior. The simulation results show a shear strength increase from 572.39 kPa to 2059.26 kPa, exhibiting a trend consistent with experimental findings. The shear failure mode manifests as a characteristic X-shaped shear band distribution, while at high confining pressures, shear fracture propagation is effectively inhibited, enhancing the overall structural stability. Furthermore, increasing confining pressure promotes denser interparticle contacts, with contact numbers increasing from 16,140 to 18,932 and the maximum contact force rising from 12.19 kN to 59.83 kN. The quantity and frequency of both strong and weak force chains also increase significantly, further influencing the mechanical response of the material. These findings provide deeper insights into the mechanical behavior of rockfill materials under varying confining pressures and offer theoretical guidance and engineering references for dam stability assessment and construction optimization.

Typical soil solidifiers, such as ordinary Portland cement, have a limited solidification effect when used as solidifiers, and they can cause significant environmental pollution during the manufacturing phase. Therefore, a relatively green and environmentally friendly solution based on magnesium sulfate cement (BMSC) is explored as a solidifying agent for solidifying the soil. The present paper undergoes a systematic compaction experiment, an unconfined compressive strength test, and an unconsolidated undrained triaxial shear parameters test of BMSC solidified soil with different magnesium oxide (MgO) contents when BMSC was used as the soil stabiliser and the physical properties of BMSC solidified soil were analysed by the techniques ofX-ray diffraction (XRD), scanning electron microscopy-energy spectrometry (SEM-EDS), XAn analysis was conducted on the mechanical properties and microstructure of BMSC solidified loess. When the molar ratio is determined, the maximum dry density increases with the increasing magnesium oxide doping. The results indicate that the compressive strength of BMSC solidified loess increases with the increase in the MgO content. Specifically, the compressive strength of the 6 % BMSC solidified loess specimen increased by 528 % compared with that of the pure loess specimen. Moreover, the maximum deviation stress increased by 236.54 %, while the cohesion and internal friction angle increased by 221.89 % and 44.27 %, respectively. The XRD and-ray computed tomography (X-CT), and mercury intrusion porosimetry (MIP). SEM/EDS analyses revealed a great number of 517 (5Mg(OH)2-MgSO4-7H2O) whiskers crisscrossing between the soil particles, which made the microstructure of the BMSC solidified loess specimen denser. The MIP results showed that the macropores and porosity reduction decreased from 43.30 % of the pure loess to 37.01 % in the 6 % BMSC solidified soil specimen. Similarly, the X-CT results revealed a higher pore density and larger porosity in pure loess.

To investigate the mechanical properties of frozen peat soil derived from Dianchi Lake's lacustrine deposits, a low-temperature triaxial shear test was conducted under various influencing factors, utilizing an improved TSZ-2 fully automatic strain control instrument. This study aimed to examine the mechanical behavior of frozen peat soil at different temperatures, confining pressures and moisture levels. Additionally, the binary medium model theory was introduced to analyze the deviatoric stress-strain relationship in frozen soil. The test results indicate that as strain increases, the deviatoric stress-strain curve divides into three stages: linear-elastic, elastic-plastic and stable stages. The volume deformation primarily involves bulk expansion, and the deformation characteristics of frozen peat soil can be explained using a binary medium model. The peak strength of frozen peat soil is positively correlated with confining pressure and moisture content, but negatively correlated with temperature. In the experimental setup, the impact of confining pressure on strength initially rises and then declines, while moisture content exhibits higher sensitivity to strength. Cohesion increases as temperature decreases, and the internal friction angle fluctuates between 20.56 degrees and 24.89 degrees. Based on the simplified binary medium model, the equations suitable for frozen peat soil are constructed and the results are verified with good applicability.

Dynamic consolidation is widely applied in the consolidation of soft soil foundation, though there is no in-depth subdivision research on the mechanism of dynamic consolidation of coastal soft soil foundation, and there is no independent, complete, theoretical system to support engineering practice. The effects of dynamic consolidation replacement rates on the shear strength of coastal soft soil were studied by the dynamic consolidation replacement undrained shear (CU) tests. CU tests were conducted for each set of samples under four confining pressures of 50 kPa, 100 kPa, 200 kPa, and 300 kPa, stress-strain curves and effective stress paths were obtained, and then shear strength parameters at different displacement rates were determined: effective cohesion and effective internal friction angle. The effective cohesion decreases, while the effective internal friction angle increases, with the increment of displacement rate. The shear strength of coastal composite soil is improved with the rising displacement rate, and the effects of multi-pile displacement on the shear strength of coastal soft soil are more significant at the same displacement rate. There is a quantitative power function relationship between the pile-soil interaction coefficient and displacement rate of coastal composite soil. Based on the test results, a modified formula for the shear strength parameters of dynamic tamper-replaced coastal soft soil is proposed.

Mechanical adhesion among lunar regolith particles significantly influences the shear characteristics of lunar regolith. However, experimental limitations on Earth and challenges in capturing particle-scale information obscure the microscopic mechanisms of adhesion and its interaction with other particle properties, such as shape. This study employs the Discrete Element Method to bridge this gap by incorporating mechanical adhesion and simplifying the particle shape effect. Numerical triaxial shear tests were performed on representative volume elements under densities representative of lunar surface. The study introduced a simplified shape parameter, the rolling friction coefficient mu r, r , representing particle 3D sphericity, which ranged from 0.025 to 1.6. Additionally, the particle surface energy density gamma was adjusted from 0 to 1.28 x 10-- 2 J/m2 2 to model the effects of mechanical adhesion. Stress-strain relationships, friction angles, and microscale mechanics parameters were thoroughly analyzed. Simulation results reveal that under low stress, the e c-ln p relationship remains linear, consistent with critical state sand theory. Significant variability in macro properties is influenced by micro-Newton adhesive forces and rolling friction coefficients (0.1-0.8), particularly in particles with notable irregularities, where adhesion profoundly affects mechanical properties, requiring precise calibration. This research advances the understanding of the shear behavior of lunar regolith, providing critical insights for future simulations and experimental designs.

Malan loess possesses unfavourable engineering mechanical properties that may vary depending on the geological context in which it exists. In the context of roadbed loading, the structural characteristics of the loess roadbed often result in uneven settlement, which significantly impacts transportation safety. To investigate the dynamic behaviour of loess under the influence of vehicle loading, groups of dynamic rebound modulus tests were conducted using a dynamic triaxial apparatus. Three key aspects are highlighted: compaction degree, moisture content and stress state. The results reveal that the dynamic rebound modulus of loess tends to increase with higher compaction degrees, decrease with increased moisture content and rise under greater confining pressure. For Maran loess, the water content has the greatest influence on its physical and mechanical properties. Under conditions of a confining pressure of 60 kPa and a deviatoric stress of 30 kPa, as the moisture content increased from w = 9% to w = 18%, the minimum dynamic rebound modulus decreased by 63%. We carried out these tests using a dynamic triaxial apparatus. The outcomes of our investigations reveal several noteworthy findings. Specifically, we observe that the dynamic rebound modulus of loess tends to increase with higher compaction degrees, decrease with increased moisture content and rise under greater confining pressure. image

A large-scale triaxial shear test was performed on a waste slag dam created from the accumulation of waste slag during the construction of a pumped-storage power station. By integrating previous experience, the particle breakage index was refined to study the relationship between particle breakage and the deformation strength characteristics of the soil-rock mixture under different dry densities and stress states. The results show that as the confining pressure increases, various dry densities enhance particle breakage, leading to a transition from initial dilatancy to shear shrinkage in the soil-rock mixture. This change results in a decrease in the nonlinear internal friction angle and a decrease in the shear strength. This research explores the shear failure mechanism caused by the breakage of soil-rock mixtures. Examination of the particle grade before and after shearing shows that the extent of particle breakage expands with higher confining pressure, especially within the 20 similar to 60 mm grain size range. The fractal dimension is calculated concurrently, showing a strong correlation with the breakage index. The concepts of the phase transition stress ratio and failure dilatancy ratio were applied to describe the deformation characteristics. Experimental results demonstrate that the influence of the phase transition stress ratio on the dilatancy becomes more significant with increased dry density, yet this effect diminishes with higher confining pressure. As the breakage index increases, the failure dilatancy rate decreases following a power function, resulting in a gradual reduction in the dilatancy phenomenon. Considering the substantial influence of clay particles on the cohesion of the soil-rock mixture and the negligible effect of breakage on fine particles, it is proposed that the cohesion remains unchanged for determining the friction parameter. With increasing breakage index, the internal friction angle decreases nonlinearly, weakening the shear strength. This analysis shows that the refined particle breakage index effectively captures the particle breakage characteristics of soil-rock mixtures, providing valuable insights into the deformation and strength characteristics of engineering structures affected by particle breakage.