Understanding the temperature-dependent behavior of sands is essential for geotechnical engineering applications, especially in environments with long-term temperature variations. This study investigates the effects of temperature (T) on the shear strength and creep deformation (Delta epsilon CP) of KMUTT and Hostun sands through a series of consolidated drained triaxial compression (CDTC) tests. Monotonic loading (ML) and sustained loading (SL) schemes were applied to evaluate shear strength and creep behavior under various stress levels (SL) and temperatures. The temperature effect parameter (Af) was introduced to quantify the reduction in shear strength at elevated T relative to a reference temperature (T0 = 30 degrees C). Experimental results show that shear strength decreases as temperature increases, with Hostun sand being more temperature-sensitive than KMUTT sand. Under SL, significant Delta epsilon CP was observed, increasing with both SL and T, while resumption of shearing after SL did not affect peak shear strength. A hyperbolic empirical equation was developed to predict Delta epsilon CP for a given creep duration (Delta tCP), SL, and T, incorporating temperature effects via Af. The model was validated with experimental results and showed strong predictive capability, especially during the primary creep stage. However, discrepancies appeared at high SL, where secondary creep effects became more pronounced. The proposed model offers a practical framework for predicting long-term creep deformation in sands under temperature variations, enhancing geotechnical design in thermally influenced environments.

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/).

The study of the compression characteristics of loess in seasonal regions involves analyzing the mechanical properties and mesoscale damage evolution of intact loess subjected to dry-wet freeze-thaw cycles. This study meticulously examines the evolution of the stress-strain curve at the macroscale and the pore structure at the mesoscale of loess by consolidation and drainage triaxial shear tests, as well as nuclear magnetic resonance (NMR), under varying numbers of dry-wet freeze-thaw cycles. Then, utilizing the Duncan-Chang model (D-C), the damage model for intact loess is derived based on the principles of equivalent strain and Weibull distribution, with testing to verify its applicability. The results indicate that the stress-strain curve of undisturbed loess exhibits significant strain softening during the initial stage of the freeze-thaw dry-wet cycle. As the number of cycles increases, the degree of strain softening weakens and gradually exhibits a strain-hardening morphology; the volume strain also changes from dilatancy to shear contraction. According to the internal pore test data analysis, the undisturbed loess contributes two components to shear strength: cementation and friction during the shear process. The cementation component of the aggregate is destroyed after stress application, resulting in a gradual enlargement of the pore area, evidenced by the change from tiny pores into larger- and medium-sized pores. After 10 cycles, the internal pore area of the sample expands by nearly 35%, indicating that the localized damage caused by the dry-wet freeze-thaw cycle controls the macroscopic mechanical properties. Finally, a damage constitutive model is developed based on the experimental phenomena and mechanism analysis, and the model's validity is verified by comparing the experimental data with theoretical predictions.

The shape of particles significantly influences their mechanical properties, making accurate shape modeling crucial in numerical simulations. This paper proposes a framework for generating particles by applying improved spherical harmonic reconstructions to convex hull surfaces. The framework integrates mesh refinement tech- niques to enhance mesh resolution, enabling the generation of finer surface details than 3D laser scanning. Three parameters are introduced: Delta K1, which controls roundness; Delta K2, which governs roughness; and Rd, which represents the boundary between roundness and roughness in spherical harmonic reconstructions. Introducing these parameters not only allows independent control over the three levels of shape (form, roundness, and roughness) but also enhances the flexibility of the method, enabling the generation of various particle shapes. Granular assemblies with varying roundness and roughness distributions are generated and applied in discrete element method (DEM) simulations of triaxial shear. The results show that roundness is negatively correlated with the peak friction angle, while roughness is positively correlated. The proposed method enhances the ability to generate complex particle shapes, offering a practical tool for modeling and simulating granular materials.

The granular and natural characteristics of soil introduce size effects to its deformation and strength properties. Therefore, investigating the phenomenon of strain localisation in soil requires a multi-scale characterisation. This study examined the intrinsic scale patterns in samples with different sizes of reinforcing particles through triaxial compression tests. Additionally, the formation mechanism of microscopic shear bands was investigated using numerical simulation methods. Drawing from the soil cell model theory, the average strain energy release coefficient was introduced to validate the transformation of the overall strain energy of the specimen after reaching the peak stress. This reflects the progressive initiation and competitive process of multiple bands. The results indicate that samples with different sizes and types of reinforcing particles exhibit various failure patterns, including single-type, 'x'-shaped, 'v'-shaped, parallel and others. The soil exhibits size effects, with the ratio of intrinsic scale to particle size decreasing as the size of reinforcing particles increases. Prior to the stress peak, non-elastic dissipation energy begins to increase, indicating the initiation of plastic deformation in the soil. Localised strain zones are activated, and after the peak, there is a sharp increase in stress within the shear bands, accompanied by rebound outside the band.

The artificial ground freezing (AGF) method is a frequently-used reinforcement method for underground engineering that has a good effect on supporting and water-sealing. When employing the AGF method, the mesoscopic damage reduces the strength of the frozen sandy gravel and consequently affects the bearing capacity of the frozen curtain. However, a few studies have been conducted on the mesoscopic damage of artificial frozen sandy gravel, which differs from fine-grained soil due to its larger gravel size. Therefore, based on triaxial compression tests and CT scanning tests, this paper investigates both the mesoscopic damage mechanism and variations in artificial frozen sandy gravels. The findings indicate that there are contact pressures between gravel tips within the frozen sandy gravel, with damage primarily concentrated around these gravels during incompatible deformation within a four-phase medium consisting of ice, water, soil, and gravel. Furthermore, numerical simulation validates that failure typically initiates at delicate contact surfaces between gravel and soil particles. For instance, when the axial strain reaches 8%, the plastic strain at the location of gravel contact reaches 4.6, which significantly surpasses most of the surrounding plastic strain zones measuring around 1.3. Additionally, the maximum local stress within the soil sample is as high as 48 MPa. This failure event is distinct from viscoplastic failure observed in frozen fine-grained soil or brittle failure seen in frozen rock. The findings also indicate that the mesoscopic damage is about 0.3 when the axial strain is 10%. The study's findings can serve as a valuable guide for developing finite element models to assess damage caused by freezing in sandy gravel using AGF method.

The influence of mechanical loading paths on the characteristics of gap-graded granular assemblies was investigated using the discrete element method (DEM). Dense and loose gap-graded assemblies with finer fraction content, f(c), ranging from 0-100% were prepared and subjected to drained triaxial compression and extension loading paths. After examining key macroscale quantities, micromechanical analyses were conducted to elicit the particle-scale characteristics including the evolution of the fabric of the assemblies under the different loading paths. The results of the DEM analysis confirm the validity of the Mohr-Coulomb failure criteria at the critical state. While the mobilised friction angle at the peak is higher under extension than in compression, no significant difference was obtained in the critical state friction angle for both loading paths. Despite the higher mean stress transmitted by the gap-graded assemblies under compression in comparison with extension, the contribution of the finer particles to the total mean stress is not significantly influenced by the loading paths. Our data show that the variation in the fabric of granular assemblies under different loading paths does not always stem from an initial inherent anisotropy. Fabric anisotropy is marginally higher under extension than in compression despite having an initial isotropic fabric.

In slopes and embankments, soil elements are often anisotropically loaded and the sustained stress ratio SR may vary a lot. The understanding of the influence of SR on the small-strain shear modulus G0 of sands prior to failure is a practical concern that remains inadequately understood in the existing literature. This study aims to address this knowledge gap through a meticulously designed experimental program. The testing program encompasses three quartz sands with differing particle shapes and a diverse set of principal stress ratios produced via drained triaxial compression. By employing bender elements embedded within the apparatus, elastic shear waves are generated, enabling the measurement of G0 from isotropic stress states to anisotropic stress states. A careful evaluation and comparison of existing anisotropic G0 models in the literature is also conducted, and the potential limitations when subjected to elevated SR levels are noted. A new, unified model is proposed to effectively characterize G0 of different sands subjected to a wide range of triaxial compression states and it is validated using literature data.

The complex distribution characteristics of root-soil composites pose challenges in understanding their mechanical behaviour during conservation tillage. This study aims to analyse mechanical parameters of root-soil composites at different soil depths, considering root distribution, and establish an empirical critical state model. Three layers were defined based on root density distribution: Shallow Aggregated Root Zone (SARZ: 0-60 mm), Middle Enriched Root Zone (MERZ: 60-150 mm), and Deep Extended Root Zone (DERZ: 150-210 mm). Triaxial tests revealed varying shear strengths, with MERZ exhibiting the highest and SARZ the lowest. The Duncan-Chang model parameters, initial modulus of deformation, and initial Poisson's ratio were significantly influenced by soil depth, mirroring shear strength trends. An empirical formula incorporating soil layer depth into the Duncan-Chang model was proposed. Critical state stress ratios for SARZ and MERZ were determined as 0.93 and 1.11, respectively, quantifying their relationship with soil depth and root distribution. This study provides theoretical and parameter support for understanding the failure mechanism of root-soil composites.

The existing lunar exploration activities and associated equipment interactions are limited to the surface environment, where the stress state of the lunar regolith is significantly lower than that in laboratory tests conducted on Earth. To address this, this paper proposes a new framework for discrete modeling of large-scale triaxial tests on lunar regolith under low confining pressure. The framework incorporates particle shapes from the Chang'E-5 mission (CE-5) and flexible boundary conditions. Firstly, the shape characteristics of the lunar regolith particles were adopted in the Discrete Element Method (DEM) model to reproduce the mechanical properties of the lunar regolith as accurately as possible. Then, experiments with varying membrane particle stiffness ratios were conducted to explore the effect of the rubber membrane's properties on the mechanical characteristics of lunar regolith under low effective confining pressure. Topological Data Analysis (TDA) tools from persistent homology were utilized to quantify the dynamic response of particles during the onset and development of strain localization. The results indicate that under low effective confining pressure, selecting appropriate rubber membrane types is crucial for accurately determining the mechanical properties of lunar regolith. (c) 2024 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.