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.

Foamed lightweight soil is widely used in subgrade engineering as a lightweight, high fluidity material. However, due to the use of cement as the main raw material, its cost is relatively high. Therefore, the preparation of foamed lightweight soil by mixing muck excavated at the project site with iron ore tailings (IOT) is not only helpful to reduce costs, but also can promote the efficient and comprehensive utilization of inactive solid waste. In this paper, the fluidity, wet density, compressive strength and specific strength of muck-IOT foamed lightweight soil with different content were tested, and the optimal mixing ratio was selected according to the engineering specifications. Then, through uniaxial and triaxial compression tests, the strength and deformation characteristics of muck-IOT foamed lightweight soil under different dosage, wet density and confining pressure conditions were studied. Finally, the influence mechanism of muck and IOT on the strength and structure of foamed lightweight soil was revealed through Scanning Electron Microscope (SEM) analysis. The research results show that the wet density of foamed lightweight soil prepared by the optimal mixing amount (20% muck and 10% IOT) is 894 kg/m3, and the uniaxial compressive strength is 4.6 MPa. While meeting the requirements of fluidity, the mixing amount of solid waste is higher, with the specific strength increased by 28.12%. In the triaxial compression test, for every 100 kg/m3 increase in wet density, the peak strength and residual strength increase by 1.30 MPa and 1.00 MPa, respectively; For every 200 kPa increase in confining pressure, the peak strength and residual strength increase by 0.27 MPa and 0.32 MPa, respectively. In addition, the shear strength levels of muck-IOT foamed lightweight soil under different normal stress conditions under different wet densities were determined by establishing the linear equations of c and phi related to the wet density. From the microstructure, it can be seen that the pores in the muck-IOT foamed lightweight soil are evenly distributed, resulting in a denser structure and reduced stress concentration, which significantly enhances the material's compressive strength.

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.

Fujian River sand (FJS) is a complex mixture of minerals and rock fragments shaped by the dynamic geological history of Fujian province, China. The macro-micro mechanical responses of FJS under triaxial shear were carefully investigated through the X-ray tomography-based in situ triaxial test. By utilising the particle tracking strategy with the signature of histograms of orientation, both intact and crushed FJS particles can be successfully recognised and tracked at different stages of axial strain. It is found that (a) smaller particles are more likely to crush than larger ones, and the crushed particles have more irregular particle shapes than the original set of particles; (b) the coordination number, fabric anisotropy, 3D rose map, and particle displacement are found to highly correlate to the phase transition point from volumetric contraction to dilation; (c) the sample deformation is found to be uniform at the early stage, and then it starts to spread from the boundaries to the inner part and finally develops into an inclined shear band; (d) locations of particle breakage within the granular assemblage show an overall sporadic and irregular pattern throughout the shearing process, which is not strongly correlated with the shear band that has developed, even at large strains.

The study of dredged fill in Guangdong (GD), China, is of great significance for reclamation projects. Currently, there are relatively few studies on dredged fill in Guangdong, and there are many differences in the engineering characteristics of dredged fill foundations formed through land reclamation and natural foundations. In order to have a more comprehensive understanding of the physico-mechanical properties of blowing fill in the coastal area of GD and to understand the effect of its long-term creep row on the long-term settlement and deformation of buildings, the material properties, microstructure, elemental composition, triaxial shear properties, and triaxial creep properties of dredged fill in Guangdong were studied and analyzed through indoor geotechnical tests, scanning electron microscopy (SEM), X-ray diffraction (XRD), and conventional triaxial shear tests and triaxial creep tests. The test results showed that the Guangdong dredged fill is characterized by a high water content, high pore ratio, and high-liquid-limit clayey sand, and the mineral composition is dominated by quartz and whitmoreite. The scanning electron microscopy results showed that the particles of the dredged fill showed an agglomerated morphology, and the surface of the test soil samples had scaly fine flakes and a fragmented structure. In the triaxial shear test, the GD dredged fill showed strain hardening characteristics, and the effective stress path showed continuous loading characteristics; the consolidated undrained shear test showed that the GD dredged fill had shear expansion characteristics under low-perimeter-pressure conditions. It was found that, with an increase in bias stress, the axial strain in the consolidated undrained triaxial creep test under the same perimeter pressure conditions gradually exceeded the axial strain in the consolidated drained triaxial creep test. The results of this study are of theoretical and practical significance for further understanding the mechanical properties of silty soils in the region and for the rational selection of soil strength parameters in practical engineering design.

Sugarcane bagasse ash is a kind of agricultural waste with a large quantity and good volcanic ash reactivity, it is necessary to find a way to reasonably utilize it to prevent environmental pollution caused by long-term accumulation. In this paper, the effect of sugarcane bagasse ash on the short-term mechanical properties of coastal cement soil were studied, and unconfined compressive tests and triaxial shear tests were carried out. The sugarcane bagasse ash content was set to 0 %, 1 %, 2 %, 3 %, 4 % and 5 %, respectively, the cement content was set to 5 %, and the curing age was set at 7d. The test results show that sugarcane bagasse ash can effectively improve the unconfined compressive strength and triaxial shear strength of cement soil, exhibiting a trend of increasing first and then decreasing with the increase of its content. When the sugarcane bagasse ash content is 1 %, the unconfined compressive strength reaches the maximum value of 2040 kPa, which is 56 % and 8 % higher than that of cement soil with 5 % and 7 % cement content, respectively. Compared with cement soil with 5 % cement content, the triaxial shear strength increases by 12 %similar to 17 %, the internal friction angle phi and cohesion c increases by 3 %similar to 8 % and 2 %similar to 11 %, respectively. The SEM test results show that the addition of bagasse ash can promote the hydration of cement to produce hydrated calcium silicate and other hydration products, fill the internal pores of the sample, and make the microstructure of the modified cement soil tend to be dense. The research results provide a reference for the application of sugarcane bagasse ash modified cement soil in practical engineering.