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.

Laboratory experiments have shown that the proportional shearing of granular materials along arbitrary strain path directions will lead to stress states that converge asymptotically to proportional stress paths with constant stress ratios. The macro- and microscopic characteristics of this asymptotic behaviour, as well as the existence of asymptotic states exhibiting a constant stress ratio and a steady strain-rate direction, have been studied using the discrete element method (DEM). Proportional shearing along a wide range of strain-rate directions and from various initial stress/density states has been conducted. The simulation results suggest that general contractive asymptotic states (except for isotropic states) do exist but may be practically unattainable. Dilative strain path simulations, on the other hand, result in continuously changing stress ratios until static liquefaction occurs, indicating the absence of dilative asymptotic states. Despite this difference, a unique relationship between the stress increments and the current stress ratio gradually emerges from all strain path simulations, regardless of strain path direction and initial stress/density conditions. At the particle scale, the granular assembly sheared along proportional strain paths exhibits a constant partition ratio between strong and weak contacts. Although general proportional strain paths are associated with changing geometric and mechanical anisotropies, the rates of change in these anisotropies for contractive strain paths are synchronised to maintain a constant ratio of their contributions to the mobilised shear strength of the material, with a higher proportion being contributed by geometric anisotropy for more dilative strain paths.

Construction and Demolition Wastes (CDW) serves as an effective filler for highway subgrades, demonstrating commendable performance characteristics. The efficient utilization of CDW not only contributes to environmental sustainability but also yields significant economic benefits. This study employs discrete element simulation to develop a triaxial sample model comprising particles with four distinct levels of sphericity. By varying the combinations of sphericity, brickconcrete ratio, and void ratio, triaxial simulation tests are conducted, and the critical state soil mechanics framework is applied to fit the critical state line (CSL) of the samples. The results indicate that sphericity, brick-concrete ratio, and void ratio substantially influence the macroscopic mechanical properties of CDW. Notably, as sphericity increases, the peak deviatoric stress of the samples decreases, and significant volume deformation occurs. The slope of the CSL in the q-p ' plane diminishes, while the slopes of both forms of the CSL in the e-log p ' plane increase. Furthermore, a decrease in the brick-concrete ratio enhances the anti-deformation and compressive capacities of the samples. As the brick-concrete ratio decreases, both the slopes and intercepts of the CSL in the e-log p ' plane exhibit an upward trend. Conversely, an increase in the void ratio leads to a reduction in the overall strength and anti-deformation capacity of the specimens, an increase in the compressibility of the specimen volume, an elevation of the CSL slope on the q-p ' plane, and a gradual increase in both the slope and intercept of the semilogarithmic form of the CSL on the e-log p ' plane, as well as a gradual increase in the slope of the power-law form of the CSL.

Offshore structures typically experience multiple storms during their service life. The soil around the foundations of offshore structures is subjected to cyclic loading during storm and reconsolidates between storms. Therefore, it is essential to understand the fundamental soil behaviour under episodic cyclic loading and reconsolidation to evaluate the long-term serviceability of offshore foundations. This paper presents experimental results of a comprehensive suite of cyclic DSS tests on a normally consolidated silty clay. The tests explore the soil response under different cyclic loading patterns (e.g., one-way or two-way), different cyclic amplitudes and number of cycles. A theoretical model, which combines the conventional cyclic contour diagram approach and principles of the critical state soil mechanics, is proposed and validated for predicting the cyclic soil response during undrained cyclic loading and hardening after reconsolidation. The model proposed in this paper paves a critical step for developing long-term soil-structure interaction models that are fundamentally linked to soil element level responses.

One of the main problems of carbonate sands is the fragile nature of particles and their susceptibility to breakage. Carbonate sands are affected by volumetric strain even at low stress levels, which is not the case with silicate sands. By defining a simple breakage model, the current study develops an elastoplastic critical state constitutive model that considers the impact of particle breakage on the mechanical behavior of carbonate sands. The particle breakage model depends on mean effective stress and critical breakage stress, which is assumed to correspond with the precompression pressure of soil in the oedometer test. In the proposed model, critical state line movement with the breakage parameter (alpha) considers the particle breakage effect. Based on the unified clay and sand model (CASM), a novel dynamic yield surface with a shape parameter affected by particle breaking has been created. Certain modifications are made to the modified Cam-Clay stress dilatancy to predict the behavior of carbonate sand. The current model has only ten parameters that simulate the carbonate sands' behavior even at high-stress levels without any breakage test. Experimental data with different soil densities, loading stress paths, and stress levels were compared with the model, and the results demonstrated satisfactory conformance.

Accurate modeling of soil behavior under seismic conditions is critical for understanding and mitigating earthquake-induced hazards. In this study, the Dyna-Simhypo model, an enhanced hypoplastic framework incorporating the intergranular strain tensor, is integrated with smoothed particle hydrodynamics (SPH) method for the first time to simulate co-seismic large deformation processes of slopes. The model's performance is validated through cyclic triaxial tests, seismic wave propagation analysis, and large-scale seismic slope simulations. Compared to the original Simhypo model, it eliminates ratcheting and reliably captures shear modulus reduction, damping buildup, and progressive soil degradation under cyclic loading. These advancements enable precise site response evaluations and accurate slope instability predictions, offering a robust tool for seismic hazard assessment.

In this paper, the thermodynamics of granular material is developed to get constitutive relations for unified modelling of undrained viscoplastic flow behavior with complex combined effects of state, rate, time, and path. The proposed formulations of energy storages and dissipations lead to the state-dependent hyperelasticity with an elastic instable region and the viscoplasticity with considerations of the granular kinetic flow. Subjected to strict thermodynamic restraints, a generalized law of viscoplastic shear flow is proposed for granular material as the combination of state-based and rate-based viscoplastic flows, which predictively captures the diversity of undrained granular flow pattern with elastic-plastic coupled non-coaxialities among stresses, (total/ viscoplastic/elastic) strains, and their increments. The viscoplastic flow is also linked with the granular temperature that accounts for the granular kinetic fluctuation varying from dilative dense flow to large unlimited flow under shear-induced static liquefaction. This enables predictions of the creep and the stress relaxation as well as the over- and -under shooting of stress under stepwise changes in strain rate. The model is well validated by predicting the flow potential, phase transformation, critical state, and rate/time effects under undrained conventional triaxial shearing and simple shearing for Toyoura sand, which are strongly related to the void ratio, the confining pressure, the shear stress, and the shear mode.

Crushable porous soils, such as volcanic pumice, are distributed worldwide and cause a variety of engineering problems, such as slope hazards. The mechanical properties of these soils are complicated by their high compressibility due to voids in the particles themselves and changes in the soil gradation due to particle crushing. They are usually classified as problematic soils and discussed separately from ordinary granular soils, and their behaviour is not systematically understood. In this study, isotropic and triaxial compression tests were conducted on artificial pumice in order to determine the relationship between the mechanical properties and the particle crushing of crushable porous granular materials. The results showed that the mechanical behaviour of artificial pumice, representative of such materials, can be explained using a particle crushing index, which is related to the degree of efficient packing. Furthermore, a new critical state surface equation was proposed. It is applicable to crushable porous granular materials and shows the potential for expressing the critical state or isotropic consolidation state of such materials as a single surface in a three-dimensional space consisting of three axes: the stress - void ratio - crushing index. The validity of this new equation was confirmed by applying it to natural pumice from previous research. (c) 2025 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BY- NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

This study investigated the hydraulic and mechanical behaviors of unsaturated coarse-grained railway embankment fill materials (CREFMs) using a novel unsaturated large-scale triaxial apparatus equipped with the axis translation technique (ATT). Comprehensive soil-water retention and constant-suction triaxial compression tests were conducted to evaluate the effects of initial void ratio, matric suction, and confining pressure on the properties of CREFMs. Key findings reveal a primary suction range of 0-100 kPa characterized by hysteresis, which intensifies with decreasing density. Notably, the air entry value and residual suction are influenced by void ratio, with higher void ratios leading to decreased air entry values and residual suctions, underscoring the critical role of void ratio in hydraulic behavior. Additionally, the critical state line (CSL) in the bi-logarithmic space of void ratio and mean effective stress shifts towards higher void ratios with increasing matric suction, significantly affecting dilatancy and critical states. Furthermore, the study demonstrated that the mobilized friction angle and modulus properties depend on confining pressure and matric suction. A novel modified dilatancy equation was proposed, which enhances the predictability of CREFMs' responses under variable loading, particularly at high stress ratios defined by the deviatoric stress over the mean effective stress. This research advances the understanding of CREFMs' performance, especially under fluctuating environmental conditions that alter suction levels. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

This paper presents the findings from a series of constant suction triaxial tests conducted on compacted sand and silty sand under unsaturated conditions. These tests were carried out using a fully automated double-walled triaxial cell employing the axis translation technique. The net mean stresses applied ranged from 50 to 250 kPa, while matric suctions were maintained at 0, 100, and 200 kPa. The primary objective of this study was to elucidate the mechanical behavior of the two compacted soils under triaxial conditions, particularly focusing on the influence of suction on variables such as peak stress, apparent cohesion, critical state stress, postpeak softening, and strain-induced dilatancy. The experimental results were utilized to calibrate and validate two prominent critical state-based models for unsaturated soils: the Barcelona basic model (BBM) and the Morvan model. While the BBM accurately predicted the deviatoric stress values at the critical state under controlled suction conditions, it did not adequately capture the postpeak softening behavior. Conversely, the Morvan model, after appropriate calibration and validation, successfully replicated both the critical state and postpeak behaviors, demonstrating a strong correlation between its predictions and the experimental data for both soil types.