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.

In geotechnical engineering, the development of efficient and accurate constitutive models for granular soils is crucial. The micromechanical models have gained much attention for their capacity to account for particle-scale interactions and fabric anisotropy, while requiring far less computational resources compared to discrete element method. Various micromechanical models have been proposed in the literature, but none of them have been conclusively shown to agree with the critical state theory given theoretical proof, despite the authors described that their models approximately reach the critical state. This paper modifies the previous CHY micromechanical model that is compatible with the critical state theory based on the assumption that the microscopic force-dilatancy relationship should align with the macroscopic stress-dilatancy relationship. Moreover, under the framework of the CHY model, the fabric anisotropy can be easily considered and the anisotropic critical state can be achieved with the introduction of the fabric evolution law. The model is calibrated using drained and undrained triaxial experiments and the results show that the model reliably replicates the mechanical behaviors of granular materials under both drained and undrained conditions. The compatibility of the model with the critical state theory is verified at both macroscopic and microscopic scales.

Mesh-free methods, such as the Smooth Particle Hydrodynamics (SPH) method, have recently been successfully developed to model the entire wetting-induced slope collapse process, such as rainfall-induced landslides, from the onset to complete failure. However, the latest SPH developments still lack an advanced unsaturated constitutive model capable of capturing complex soil behaviour responses to wetting. This limitation reduces their ability to provide detailed insights into the failure processes and to correctly capture the complex behaviours of unsaturated soils. This paper addresses this research gap by incorporating an advanced unsaturated constitutive model for clay and sand (CASM-X) into a recently proposed fully coupled seepage flow-deformation SPH framework to simulate a field-scale wetting-induced slope collapse test. The CASM-X model is based on the unified critical state constitutive model for clay and sand (CASM) and incorporates a void-dependent water retention curve and a modified suction-dependent compression index law, enabling the accurate prediction various unsaturated soil behaviours. The integration of the proposed CASM-X model in the fully coupled flow deformation SPH framework enables the successful prediction of a field-scale wetting-induced slope collapse test, providing insights into slope failure mechanisms from initiation to post-failure responses.

Anisotropic soils exhibit complex mechanical behaviours under various loadsing conditions, e.g., reversible dilatancy, three-dimensional failure strength, fabric anisotropy, small-strain stiffness, cyclic mobility, making it difficult to comprehensively capture these characteristics within a single constitutive model. Failure to capture anisotropic soil behavious may result in poor predictions in geotechnical engineering. Hence, to provide a unified prediction for the mechanical responses of anisotropic sand and clay under both monotonic and cyclic loading conditions, a fabric-based anisotropic constitutive model, i.e., the CASM-CF, is developed within the framework of the standard Clay and Sand Model (CASM) in this paper. Effects of small-strain stiffness and anisotropic elasticity are incorporated into the stiffness matrix to capture the stiffness variation over a wide strain range and reversible dilation. The fabric tensor defined by particle orientation and its evolution law are integrated into the CASM-CF model through the Anisotropic Transformed Stress (ATS) method. The plastic modulus is modified by considering cyclic loading history and stress reverse to better predict the mechanical responses of soils when subjected to cyclic loadings. The newly proposed model is employed to predict the mechanical behaviours of clay and sand under various strain scales and stress paths, including monotonic, cyclic, proportional, and non-proportional loading conditions, in the literature. Conclusions can be drawn that the model performs satisfactorily under various stress paths, and it has the potential to be used in the analysis of practical geotechnical applications of wide range.

This paper presents a constitutive model for biotreated sand, developed within the framework of thermodynamic theory, to describe its mechanical behavior under undrained shear conditions. The model incorporates a reinforcement index and a hardening index to account for bonding effects. Undrained triaxial shear tests are conducted to validate the constitutive model. The results demonstrate the model's capacity to accurately predict the undrained shear behavior of biotreated sand under various reinforcement levels and initial confining pressures. It effectively captures the evolution of deviatoric stress, pore pressure, and stress paths. Furthermore, the model accounts for energy dissipation and the degradation of inter-grain bonding during undrained shearing, providing a theoretical foundation for the engineering application of biotreated sand.

The overconsolidation ratio (OCR) is a critical factor in determining the mechanical behaviour of overconsolidated clays. On the basis of the three requirements for the peak strength line, a continuous and smooth peak strength line is constructed from the perspective of the peak stress ratio, and then a new yield function for overconsolidated clays is developed. The developed yield function in the stress space is characterized by an elliptical curve. The evolution of the developed yield function in the stress space is captured by a new hardening parameter, which is constructed by integrating the proposed peak strength surface with the subloading surface concept. By combining the developed yield function with the non-orthogonal plastic flow rule, a non-orthogonal elastoplastic constitutive model of overconsolidated clays is established to consider the influence of the OCR on strength and deformation. The proposed model requires seven material parameters, all of which have a clear physical meaning and can be easily determined via conventional laboratory tests. Three typical stress paths are employed to demonstrate the essential features of the proposed model. The effectiveness of the proposed model is confirmed by comparing the experimental data with corresponding model predictions.

Soil-rock mixtures are composed of a complex heterogeneous medium, and its mechanical properties and mechanism of failure are intermediate between those of soil and rock, which are difficult to determine. To consider the influence of different particle groups on soil-rock mixture's shear strengths, based on the mesomotion properties of the particles of different particle groups when the soil-rock mixture is deformed, it is classified into two-phase composites, matrix and rock mass. In this paper, based on the representative volume element model of soil-rock mixtures and the Eshelby-Mori-Tanaka equivalent contained mean stress principle, a model of shear constitutive of the accumulation considering the mesoscopic characteristics of the rock is established, the influence of different factors on the shear strength of the accumulation is investigated, and the mesoscopic strengthening mechanism of the rock on the shear strength of the accumulation is discussed. The results show that there is a positive correlation between the rock content, the surface roughness of the rock, the stress concentration coefficient, coefficient of average shear displacement, and the accumulation's shear strength. When the accumulation is deformed, it stores or releases additional energy than the pure soil material, so it shows an increase in deformation resistance and shear strength on a macroscopic scale.

Self-boring pressuremeter (SBPM) tests are widely used in situ investigations, due to their distinct advantage to measure the shear stress-strain-strength properties of the surrounding soil with minimum disturbance. The measured pressuremeter curve can be interpreted using analytical solutions based on the long cylindrical cavity expansion/contraction theory with relatively simple constitutive models, to derive useful soil properties (e.g., undrained shear strength of clay, shear modulus, and friction angle of sand). However, the real soil behavior is more complex than the assumed constitutive relations, and the derived parameters may differ from those obtained using more reliable lab tests. In addition, SBPM tests can be affected by other well-known factors (e.g., installation disturbance, limited length/diameter ratio, and strain rate) that are not considered in the analytical solutions. In this paper, SBPM tests are evaluated using finite-element analysis and the MIT-S1 model, a unified constitutive model for soils, to consider complex soil behavior more realistically. SBPM tests in Boston Blue Clay and Toyoura sands are simulated in axial symmetric and plain strain conditions, and the computed results are interpreted following the suggested procedures by analytical solutions. The derived parameters are compared with those from the stress-strain relations to evaluate the reliability of SBMP tests for practical application.

The mechanical behavior of structured soils is influenced by both inter-particle bonding and fabric arrangements. Existing constitutive models primarily account for soil structure through fabric arrangements. In this study, we first present experimental investigations on intact loess samples, including isotropic compression (IC), conventional consolidation undrained (CU), and consolidation drained (CD) triaxial tests, which reveal the complex structural properties of the soil. Next, we employ the work done by strain energy to comprehensively account for soil structure, incorporating both inter-particle bonding and fabric arrangements. Subsequently, a new strain work constitutive model for structured soils is presented within the critical state framework. Specifically, a linear decreasing function between strain power and mean effective stress is introduced to capture structural degradation, and a new hardening rule is derived from the relationship between strain work and mean effective stress. Compared to traditional structured soil models, the proposed model offers clear physical meaning, and its parameters are easily obtainable. The model's simulation results are validated against experimental data, demonstrating its ability to capture key mechanical and deformation characteristics, such as strain softening under CU conditions and strain hardening under CD conditions. Finally, we compare our model with the structured cam clay (SCC) model, and the results show that our model provides a better fit to the experimental data, further confirming its accuracy and effectiveness.

Cemented sand-gravel (CSG) is an innovative material for dam construction with a wide range of applications. Nevertheless, a comprehensive understanding of the dynamic properties of CSG is lacking. A series of cyclic triaxial dynamic shear tests were carried out on CSG materials to investigate their complex dynamic mechanical properties, leading to the establishment of a dynamic constitutive model considering damage. The findings indicate that both the application of confining pressure and the addition of cementitious material have a noticeable influence on the morphology of the hysteresis curve. Further research scrutiny reveals that augmenting confining pressure and gel content leads to an increase in the dynamic shear modulus and a decrease in damping ratio. Furthermore, a constitutive dynamic damage constitutive model was constructed by linking a damage element to the generalized Kelvin model and defining the damage variable D based on energy interaction principles. The theoretical formulas for dynamic shear modulus and damping ratio were adjusted accordingly. In addition, the stiffness matrix of the dynamic damage constitutive model was derived, which demonstrated its strong fitting effects in dynamic triaxial shear tests on CSG. Finally, the dynamic response and damage distribution in the dam body under dynamic loading were analyzed using a selected CSG dam in China.