Constitutive models of sands play an essential role in analysing the foundation responses to cyclic loads, such as seismic, traffic and wave loads. In general, sands exhibit distinctly different mechanical behaviours under monotonic, regular and irregular cyclic loads. To describe these complex mechanical behaviours of sands, it is necessary to establish appropriate constitutive models. This study first analyses the features of hysteretic stressstrain relation of sands in some detail. It is found that there exists a largest hysteretic loop when sands are sufficiently sheared in two opposite directions, and the shear stiffness at a stress-reversal point primarily depends on the degree of stiffness degradation in the last loading or unloading process. Secondly, a stress-reversal method is proposed to effectively reproduce these features. This method provides a new formulation of the hysteretic stress-strain curves, and employs a newly defined scalar quantity, called the small strain stiffness factor, to determine the shear stiffness at an arbitrary stress-reversal state. Thirdly, within the frameworks of elastoplastic theory and the critical state soil mechanics, an elastoplastic stress-reversal surface model is developed for sands. For a monotonic loading process, a double-parameter hardening rule is proposed to account for the coupled compression-shear hardening mechanism. For a cyclic loading process, a new kinematic hardening rule of the loading surface is elaborately designed in stress space, which can be conveniently incorporated with the stressreversal method. Finally, the stress-reversal surface model is used to simulate some laboratory triaxial tests on two sands, including monotonic loading tests along conventional and special stress paths, as well as drained cyclic tests with regular and irregular shearing amplitudes. A more systematic comparison between the model simulations and relevant test data validates the rationality and capability of the model, demonstrating its distinctive performance under irregular cyclic loading condition.

Cohesion provided by pore ice is a critical component influencing the mechanical behavior of frozen soil, as it not only cements soil particles together but also shares the external loads with them. In view the crucial role of cohesion in developing an elastoplastic model for frozen soil, this paper employs triaxial tensile strength (TTS) to characterize cohesion and proposes a TTS degradation expression driven by plastic shear strain. By directly incorporating TTS into the yield function, a framework for a Non-Orthogonal Elastoplastic (NOEP) constitutive model that accounts for cohesion degradation in frozen soil is developed. Furthermore, a hardening parameter incorporating TTS is introduced and used in conjunction with the modified yield function to determine the magnitude of the plastic strain increment. The non-orthogonal plastic flow rule is used to determine the direction of the plastic strain increment based on the modified yield function. Ultimately, by combining the elastic strain increment determined by Hooke's rule, a NOEP constitutive model incorporating cohesion degradation for frozen soil is established. The validity and rationality of the proposed NOEP model in representing the stress-strain relationship of frozen soil are confirmed through comparisons with test results of frozen soil under the triaxial compression conditions. The proposed constitutive model provides a more comprehensive and precise representation of frozen soil's response to external loading, enhancing the understanding of its shear deformation behavior and providing a robust theoretical foundation for engineering design and construction in cold regions.

This article presents the findings of a comprehensive assessment of the predictive capabilities and limitations of advanced geotechnical numerical tools utilizing two sophisticated constitutive models for sands: the hardening soil model with small strains and hypoplasticity with intergranular strain. The evaluation is based on simulations of laboratory and centrifuge tests under monotonic and cyclic loading conditions. Initially, these models were calibrated and assessed using an experimental database on Fontainebleau sand. This database encompasses a range of laboratory results, including isotropic compression, drained monotonic triaxial, and undrained cyclic triaxial tests with varying initial conditions. The models, in general, provided good representation for monotonic experiments while some discrepancies were observed in undrained cyclic experiments. Subsequently, the calibrated models were employed to replicate a series of centrifuge tests involving a pile embedded in the same sand. The pile was subjected to various episodes of monotonic and cyclic lateral loading. In general, the models accurately replicated the experimental observations from tests conducted under monotonic loading conditions. Some small discrepancies were found in pile tests subjected to cyclic loading, these were however minor when compared to issues in predicting cyclic element tests at undrained conditions.

This paper presents an efficient two-and-a-half dimensional (2.5D) numerical approach for analysing the long-term settlement of a tunnel-soft soil system under cyclic train loading. Soil deformations from train loads are divided into shear deformation under undrained conditions and volumetric deformation from excess pore water pressure (EPWP) dissipation. A 2.5D numerical model was employed to provide the dynamic stress state owing to the moving train load and the soil static stress state by the gravity effect for the determination of their accumulations. Then, an incremental computation approach combined with the initial strain approach in the framework of the 2.5D model was developed to compute the long-term deformation of the tunnel-soft soil system, considering the influence of the soil hardening due to EPWP dissipation. This approach helps to determine the distribution of the progressive settlement, transverse and longitudinal deformations in the tunnel-soil system, overcoming traditional limitations. A comparison of settlements computed using this approach with measured settlements of a shield tunnel in soft soil shows good agreement, indicating the effectiveness of the proposed approach in analysing train-induced progressive deformation of the tunnel-soil system.

Stress-strain results from high-strain rate consolidated-undrained (CU) triaxial compression tests on partially saturated kaolin clay are presented. The work addresses the scarcity of high-strain rate data for cohesive soils and provides updated strain rate coefficients for kaolin clay. It covers strain rates from quasi-static (0.01%/s) to dynamic (800%/s) regimes. Kaolin clay specimens were prepared wet of optimum using static compaction at a constant water content of 32 +/- 1% and a degree of saturation of 96 +/- 2%. The specimens were then loaded into triaxial cells and consolidated under pressures ranging from 70 to 550 kPa for 24 h prior to testing. Tests were conducted using a modified hydraulic frame, and a methodology for correcting compression data to account for inertial effects observed during high-rate testing was adopted. The data revealed significant strengthening of clays with increased strain rates, especially at low confining pressures. Lightly confined clays (sigma 3 = 70 kPa) experienced a 165% strength increase, while highly confined clays (sigma 3 = 550 kPa) showed a 52% increase. Analysis using secant moduli revealed increased stiffening with loading rate. Posttest examination of specimens revealed a decrease of shear localization with increasing strain rate, indicating that a transition in failure mode contributes to the increased strengthening and stiffening of clays at high rates. The stress-strain data were used to calibrate the semilogarithmic and power law strain hardening models, yielding lambda and beta values that decreased linearly with increasing confining pressure. Equations relating lambda and beta to confining pressure were developed for practical applications, applicable to normally consolidated clays under confining pressures up to approximately 5 atmospheres.

Consolidated-drained true triaxial tests with constant b\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$b$$\end{document} values were performed on normally consolidated cross-anisotropic kaolin clay. Isotropic stress probes were incorporated into these true triaxial tests to study the orientations of plastic strain increment vectors and positioning of the plastic potential surface at different levels of shearing. An isotropic compression test was also performed to characterize the cross-anisotropic response of the clay. Pronounced cross-anisotropy was observed in the K0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$K_{0}$$\end{document} consolidated kaolin clay during shear, particularly when the major and minor principal stresses were perpendicular and parallel to the axis of material symmetry, respectively. A simple rotational kinematic hardening mechanism incorporated into the single hardening constitutive model for soil has been found to fairly accurately simulate the evolution of anisotropy in the form of expansion and rotation of the yield and plastic potential surfaces during true triaxial shearing.

The traditional brick-firing process, characterized by high energy consumption and significant pollutant emissions, poses environmental challenges that require innovative solutions. This research addresses these challenges by reducing natural resource usage, energy consumption, and gas emissions through the production of mudbricks in which 5-10 wt% of the clayey soil is replaced by tea grounds. This approach uses waste products and efficient manufacturing techniques aimed at achieving zero carbon emissions. The meticulous selection and processing of organic waste draws inspiration from ancient practices in which plant residues were used to enhance the durability and performance of building materials. This study demonstrates that the inclusion of 10 wt% tea grounds enhances the workability of the clay by 15 %, as the lignin and hydrogen bonds in the tea rearrange the molecules, hardening the material in a similar way to the starch retrogradation process in bread. These mud- bricks provide a 25 % improvement in thermal insulation compared to standard mudbricks, potentially reducing reliance on energy-intensive heating and cooling systems by up to 20 %. It also show a 30 % enhancement in impermeability relative to mudbricks made without tea grounds, with a 10 % increase in compressive strength.

In order to explore the mechanical properties and microstructure changes of frozen saline silty clay in the Hexi region of Gansu Province, triaxial compression tests and scanning electron microscopy (SEM) analysis experiment were conducted to explore the effects of moisture content, confining pressure, and temperature on the stress-strain characteristics and failure modes of frozen soil, as well as the changes in the internal microstructure of the sample. The experimental results show that the strength of frozen sulfate saline soil first increases and then decreases with the increase of moisture content, and the maximum strength corresponds to a moisture content of 15%. The changes in confining pressure and strength have the same trend. The lower the temperature, the greater the strength of the sample. During the entire loading process, the specimens undergo a gradual transition from volume shrinkage to volume expansion. Due to the strain harden behavior of the stress-strain curve throughout the entire loading process, the failure mode of the specimens is plastic failure. The internal microstructure of the sample gradually transitions from point-point contact and edge-point contact before shearing to edge-surface contact and edge-edge contact after shearing, and the pore size inside the sample increases after shearing, with a loose arrangement of the particle skeleton. The above research conclusions can lay a certain theoretical foundation for the engineering design and construction of sulfate saline soil in cold and arid areas.

The plastic strain of calcareous sand is related to its stress path and particle breakage, rendering the hardening process complex. An expression for the stress-path-dependence factor was developed by analyzing the variations in plastic strain across different initial void ratios. A stress-path-independent hardening parameter was derived from the modified plastic work and was subsequently validated. Constant-proportion loading tests on calcareous sands confirmed the applicability of this hardening model. The results indicated that under isotropic compression, the plastic volumetric strain increased with increasing average effective stress, albeit at a decreasing growth rate. A positive linear relationship was observed between the volumetric strain modulus and relative breakage index. The proposed hardening parameter effectively captured the particle breakage and stress path effects in calcareous sand and was validated through theoretical calculations and laboratory tests, offering valuable insights into the mechanical behavior of fragile granular soils.

In cold regions, the frozen soil-rock mixture (FSRM) is subjected to cyclic loading coupled with freeze-thaw cycles due to seismic loading and ambient temperature changes. In this study, in order to investigate the dynamic mechanical response of FSRM, a series of cyclic cryo-triaxial tests were performed at a temperature of -10 degrees C on FRSM with different coarse-grained contents under different loading conditions after freeze-thaw cycles. The experimental results show that the coarse-grained contents and freeze-thaw cycles have a significant influence on the deformation properties of FSRM under cyclic loading. Correspondingly, a novel binary-medium-based multiscale constitutive model is firstly proposed to describe the dynamic elastoplastic deformation of FSRM based on the coupling theoretical framework of breakage mechanics for geomaterials and homogenization theory. Considering the multiscale heterogeneities, ice-cementation differences, and the breakage process of FSRM under external loading, the relationship between the microscale compositions, the mesoscale deformation mechanism (including cementation breakage and frictional sliding), and the macroscopic mechanical response of the frozen soil is first established by two steps of homogenization on the proposed model. Meanwhile, a mixed hardening rule that combines the isotropic hardening rule and kinematic hardening is employed to properly evaluate the cyclic plastic behavior of FSRM. Finally, comparisons between the predicted results and experimental results show that the proposed multiscale model can simultaneously capture the main feature of stress-strain (nonlinearity, hysteresis, and plastic strain accumulation) and volumetric strain (contraction and dilatancy) of the studied material under cyclic loading.