The shear behavior of gravel-block soil (GBS) is unique and significant for evaluation the failure mechanism of GBS landslide on the Qinghai-Tibet Plateau. This study focuses on interpreting the shear behavior observed in the GBS during large-scale direct shear tests conducted on a landslide in Jiacha County, Tibet, China. The tests considered coarse particle content (CPC), dry density, and moisture conditions. Additionally, a discrete element numerical model, scaled to match the laboratory testing dimensions, was developed to simulate the large-scale direct shear tests on GBS. Results indicated that an increase in CPC improves the strength of the GBS, as it enhances the framework strength through interlocking between gravel blocks and between gravel blocks and the soil mass. The critical CPC for shear failure of the GBS exhibits a decreasing trend as the dry density increases. Furthermore, particle crushing rate (PCR) of the GBS is positively correlated with CPC, vertical pressure, and dry density. The simulation results show good agreement with the test results, providing insights into the damage-shear fracture mechanism of typical GBS under large-scale direct shear tests. The research outcomes provide a theoretical basis for the prevention and control of geological hazards in the Qinghai-Tibet Plateau.

Particle crushing usually occurs in granular materials and affects their structural and mechanical properties. To investigate the mechanical behavior and crushing characteristics of heterogeneous particles, this study conducts both laboratory tests and numerical simulations for a macro-microscopic analysis of the heterogeneous particles. The laboratory tests results demonstrate that the single particle crushing strength and crushing pattern have obvious size effect. In numerical simulations, the heterogeneous crushable particle model was constructed by using Gaussian distribution and Voronoi tessellation, and the degree of heterogeneity (d) is defined as the ratio of the standard deviation to the expected value. The numerical findings demonstrate that the size effect of crushing strength is mainly attributed to heterogeneity. The degree of heterogeneity weakens the particle crushing strength. As the d value increases, the force-displacement curve of the particle exhibits stronger nonlinear characteristics, and the macroscopic failure pattern changes from brittle failure to ductile failure. Additionally, with the increase in d, the deformation coordination between child particles decreases, which leads to enhanced local stress concentration, causing a reduction in the crack initiation stress. This change causes the crack propagation mode to evolve from a sharp angle to a blunt angle, and ultimately determines the crushing strength and crushing pattern of particles. (c) 2025 Published by Elsevier B.V. on behalf of The Society of Powder Technology Japan. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

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/).

Research on the evolutionary behavior of the particle breakage processes in coarse-grained soil under the action of train load is of practical significance for subgrade construction and maintenance. However, existing studies have not addressed the prediction of particle size distribution evolution. In this paper, the MTS loading system is used to simulate the dynamic train load effect on coarse-grained soil fillers. The study analyzes the influence of dynamic stress amplitude, loading frequency, and vibration times on both the macro-characteristics and micro-characteristics of particle breakage. The characteristics of particle fragmentation in coarse soil filler under high-speed train load are elucidated. Furthermore, a predictive model for the evolution of particle size distribution curves in relation to particle content and relative particle size is established using the ZHU continuous grading curve equation. This model captures the evolution process of particle breakage characteristics in coarse-grained soil fillers subjected to high-speed train loads. The applicability of this model has been verified. Based on the grading prediction model, an integral expression for the breakage rate index is derived, and the evolution characteristics of particle breakage in coarse-grained soil fillers under the action of train load are analyzed. The results indicate that during filling, the particle breakage mode of coarse-grained soil fillers during filling is primarily characterized by fracture and fragmentation; conversely, under dynamic cyclic loading conditions, it is predominantly characterized by fracture and grinding. The breakage rate aligns with the measured results, suggesting that the breakage rate index established in this study can effectively describe the evolution process of particle breakage in railway subgrade coarse-grained soil. After the reaching one million loading cycles, both deformation and particle breakage degree in coarse-grained soil fillers tend to stabilize. Under the action of dynamic stress amplitudes ranging from 10 to 200 kPa and loading frequencies between 2 and 12 Hz, the particle breakage index stabilizes below 1.1%. These research findings contribute to a deeper understanding of the evolutionary processes affecting engineering characteristics of railway subgrade coarse-grained soils and provide a theoretical as well as experimental foundation for railway subgrade construction and maintenance.

There is substantial evidence that crushable soils (e.g., sands, gravels, rockfills, etc.) undergo particle crushing upon shearing or over creeping. To investigate the evolution of grading and particle crushing of coarse-grained materials, a series of consolidated and drained triaxial shearing and creep tests were conducted on rockfills using a large-scale triaxial apparatus. The test data from the sieve analysis test, both before and after the triaxial tests, were subjected to a comprehensive qualitative and quantitative analysis of the variation of grading or breakage index. Research findings indicate a decrease in the percentage of coarser particles in the particle components of rockfills, accompanied by an increase in the amount of particle crushing upon shearing or over creeping. Furthermore, a series of empirical expressions were proposed through nonlinear fitting of test data to characterize the relationship between the breakage index and two variables (i.e., the normalized plastic work and mean effective stress) under various confining pressures and stress levels upon shearing or over creeping. These findings can provide a scientific basis for the design, construction, and maintenance of rockfill dams or high rockfill embankments in the practical engineering application.

The shear modulus degradation curve in normalized shear modulus vs. shear strain plane presents crucial information about the cyclic and/or dynamic response of soil, especially for undrained conditions. This study introduces an analytical shear modulus degradation model specifically for carbonate sand subjected to high-amplitude cyclic loading associated with marine geostructures. Unlike hard-grain siliceous sand, carbonate is soft and crushable under low confining conditions. To address this, we utilize a generic analytical shear modulus degradation model and enhance it for carbonate sand. The model coefficients are first calibrated based on existing cyclic experiments on carbonate sand collected from various offshore regions around the world, without taking into account the particle crushing effect. Later, cyclic undrained tests are numerically simulated, accounting for the particle-crushing effect using a bounding surface plasticity soil model. The simulation results show a noticeable shift in the shear modulus degradation curves while accounting for the particle breakage compared to non-crushable sands, irrespective of cyclic stress ratio conditions. Based on the numerical simulations, the analytical model is further refined through evolving characteristics of sand gradation (i.e., coefficient of uniformity). The proposed model is validated with separate experimental results of carbonate sand subjected to different confining pressures.

Background The 2018 Hokkaido Eastern Iburi Earthquake triggered serious geodisasters, resulting in several landslides in volcanic soils depending on their geological features. However, there is limited investigation from the geotechnical viewpoint. Considering various volcanic soils are deposited in Hokkaido, Japan, it is crucial to ensure disaster prevention of infrastructures related to volcanic soils. Methods To investigate the degree of weathering, water-retention characteristics, and mechanical properties of the volcanic soil, which triggered landslides during the earthquake, called Ta-d, this study conducted laboratory tests including X-ray diffraction, water-retention, and direct shear tests under various conditions related to a type of Ta-d, saturation condition, and stress dependency. Moreover, the pore pressure of the location where the landslides occurred was monitored for over a year to investigate the effect of rainfall on the previous day of the earthquake on the landslides. Results The laboratory and field monitoring test results showed that Ta-d can be categorized into three types depending on the color and physical properties, which have different degrees of weathering and shear strengths. The water content of Ta-d was high (>100 %) throughout the year, whereas it exhibited a seasonal change due to snowfall, which covered the ground surface. Furthermore, fluctuations caused by the seasonal changes are more significant than those caused by rainfall, which indicated that the rainfall on the previous day of the earthquake was not a primary factor in the occurrence of the landslides Conclusions This study reveals the geotechnical properties of Ta-d, which has not been well known, as comparing with those of other Hokkaido volcanic soils, and gives insights into the significant factors that can potentially cause the earthquake-induced geodisasters.

Coral sand particles exhibit a wide range of shapes, which can be divided into four shapes, e.g., blocky, dendritic and rodlike, flaky, and shell debris. The particle shape of these mixtures is defined by the sphericity, concavity, aspect ratio, flatness and overall regularity, which ranges from 0 to 1. The effect of particle shape on the strength, crushing characteristics, and critical state parameter is systematically investigated through a series of triaxial drainage shear tests under different confining pressures. And the relationship between critical state parameters and mechanical parameters is established. The test results demonstrate the existence of an evident strain-hardening phenomenon in the stress-strain curve of coral sand, accompanied by a strain-softening phenomenon when the bias stress reaches its peak value. The sample is initially subjected to shear shrinkage, followed by shear expansion. The volumetric deformation of the coral sand decreased with increasing peripheral pressure. The particles are transformed from rough irregular shapes to smooth spheres as evidenced by an increase in the shape parameter. The greater the degree of irregularity in the shape of the particles, the more pronounced the resulting change in size reduction. In addition, the critical state parameter was found to be influenced by the shape of the coral sand particles and the mode of particle accumulation. The overall shear resistance of coral sand particles was found to depend on particle rearrangement in addition to particle surface roughness and interparticle friction. It is proposed that the general regularity critical state parameter equation relates the particle shape of coral sand to its critical state mechanical properties, which is of great importance to the practical application and research of coral sand in engineering, and provides an effective means of predicting mechanical properties granular materials.

Reinforcing calcareous sands with geogrids is a potentially effective method for large-scale geotechnical constructions in coastal lands. The breakable nature of polygonal calcareous sands determines the complex particlegeogrid interactions. A three-dimensional numerical model of geogrid reinforced calcareous sand (GRCS) was established to investigate the potential mechanical laws based on the discrete element method (DEM), and the reasonableness of the numerical model was verified by comparing with the indoor triaxial test. It follows that the macro-microscopic mechanical behavior of GRCS under the influence of aperture size and tensile resistance of geogrids was further investigated via effective DEM simulations. The presented results show that the decreased aperture size and increased tensile resistance are beneficial to enhance the macro-mechanical properties of GRCS, including strength, internal friction angle and pseudo cohesion. Particle crushing is mainly affected by shear strain and confining pressure. The bulging deformation of GRCS is partially suppressed due to the confining effect of geogrids. Besides, the source of strength enhancement of GRCS is revealed based on the microscopic particlegeogrid interactions, and the calculation method of horizontal and vertical additional stresses in the reinforced soil element considering the effects of tensile resistance and aperture size is further established.

Volcanic pumice, with special characteristics such as crushable particles and high water retention, is distributed throughout Japan and serves as the source layer for slope hazards characterised by post-failure gentle slope flows and long-distance flows. The aim of this study is to determine the relationship between the crushing characteristics and the mechanical properties of porous pumice, which often contributes to such disasters. As the porous pumice material, Ta -d pumice, which caused numerous slope disasters during the 2018 Hokkaido Eastern Iburi Earthquake in Japan, was collected and subjected to a series of triaxial compression tests. The grain size distribution of the pumice before all the tests was adjusted to be uniform, and the amount of crushing was quantified by measuring the grain size distribution after the tests. The results suggest that the critical state and isotropic consolidation of porous pumice can be systematically expressed in a three-dimensional space with the axes of the void ratio, mean effective stress, and degree of particle crushing. Furthermore, a gentle slope disaster with an inclination of less than 21 degrees, that had occurred at the site from which the Ta -d pumice was collected, was discussed in terms of its flow potential, showing that the flow distance can be adequately explained. (c) 2023 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).