The cumulative plastic deformation and damage evolution of frozen soil-rock mixtures under cyclic loading was studied by a dynamic triaxial instrument with real-time resistivity measurement function. A series of low- temperature cyclic triaxial tests were conducted under varying confining pressures (200 kPa, 500 kPa, 800 kPa), block proportions (0, 30 %, 40 %, 50 %), and dynamic stress ratios (0.4, 0.6, 0.8). The results reveal that the cumulative plastic deformation process can be divided into three stages, such as microcrack closure as the initial stage, crack steady growth as the middle stage, and rapid crack propagation until it fails as the final stage. Under the same number of cycles, the greater the dynamic stress is, the greater the cumulative plastic deformation is. Furthermore, a strong correlation is identified between the resistivity and the cumulative plastic deformation. With the increase of the number of cycles, the cumulative plastic deformation leads to the accumulation of internal damage, and the resistivity gradually increases. Thus, a damage evolution model based on resistivity damage variables is proposed. The model demonstrated an average fitting accuracy of 97.36 % with the experimental data.

To address the issues of significant deformation and susceptibility to liquefaction of silt under traffic loads, while also promoting the reuse of waste lignin, lignin was used to reinforce silt. A series of laboratory experiments were conducted to investigate the effects of different lignin contents and curing periods on the compressive strength of the soil. Additionally, the study analyzed the cumulative plastic deformation and excess pore-water pressure under various conditions. Using scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy, the microstructural characteristics of silt before and after lignin modification were qualitatively and quantitatively described. The experimental results indicate that lignin can significantly enhance the compressive strength of soil, and the optimal effect was observed at an 8% lignin content. At a curing age of 28 days, the strength of the treated soil was 2.65 times that of the untreated soil. The treated soil exhibited greater shear strength than the untreated soil. The addition of lignin significantly reduced the cumulative plastic deformation and excess pore-water pressure of the soil, mitigating various risks in the subgrade, such as insufficient bearing capacity and liquefaction. Lignin binds soil particles and undergoes a cementation reaction without the formation of new minerals. The cementitious material fills the voids in the soil, gradually transforming large pores into medium and small pores. Combined with the particle pores and cracks analysis system, quantitative analysis indicates that as the lignin content increased, the soil porosity gradually decreased, reaching a maximum soil compactness at an 8% admixture. The research findings can provide theoretical references for the engineering application of lignin.

We study CO2 injection into a saline aquifer intersected by a tectonic fault using a coupled modeling approach to evaluate potential geomechanical risks. The simulation approach integrates the reservoir and mechanical simulators through a data transfer algorithm. MUFITS simulates non-isothermal multiphase flow in the reservoir, while FLAC3D calculates its mechanical equilibrium state. We accurately describe the tectonic fault, which consists of damage and core zones, and derive novel analytical closure relations governing the permeability alteration in the fault zone. We estimate the permeability of the activated fracture network in the damage zone and calculate the permeability of the main crack in the fault core, which opens on asperities due to slip. The coupled model is applied to simulate CO2 injection into synthetic and realistic reservoirs. In the synthetic reservoir model, we examine the impact of formation depth and initial tectonic stresses on geomechanical risks. Pronounced tectonic stresses lead to inelastic deformations in the fault zone. Regardless of the magnitude of tectonic stress, slip along the fault plane occurs, and the main crack in the fault core opens on asperities, causing CO2 leakage out of the storage aquifer. In the realistic reservoir model, we demonstrate that sufficiently high bottomhole pressure induces plastic deformations in the near-wellbore zone, interpreted as rock fracturing, without slippage along the fault plane. We perform a sensitivity analysis of the coupled model, varying the mechanical and flow properties of the storage layers and fault zone to assess fault stability and associated geomechanical risks. (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/).

Preexisting cracks inside tight sandstones are one of the most important properties for controlling the mechanical and seepage behaviors. During the cyclic loading process, the rock generally exhibits obvious memorability and irreversible plastic deformation, even in the linear elastic stage. The assessment of the evolution of preexisting cracks under hydrostatic pressure loading and unloading processes is helpful in understanding the mechanism of plastic deformation. In this study, ultrasonic measurements were conducted on two tight sandstone specimens with different bedding orientations subjected to hydrostatic loading and unloading processes. The P-wave velocity was characterized by a similar response with the volumetric strain to the hydrostatic pressure and showed different strain sensitivities at different loading and unloading stages. A numerical model based on the discrete element method (DEM) was proposed to quantitatively clarify the evolution of the crack distribution under different hydrostatic pressures. The numerical model was verified by comparing the evolution of the measured P-wave velocities on two anisotropic specimens. The irreversible plastic deformation that occurred during the hydrostatic unloading stage was mainly due to the permanent closure of plastic-controlled cracks. The closure and reopening of cracks with a small aspect ratio account for the major microstructure evolution during the hydrostatic loading and unloading processes. Such evolution of microcracks is highly dependent on the stress path. The anisotropy of the crack distribution plays an important role in the magnitude and strain sensitivity of the P-wave velocity under stress conditions. The study can provide insight into the microstructure evolution during cyclic loading and unloading processes. (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-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

Karst collapse as a unique environmental geological hazard in karst areas, easily causes changes in surrounding water and soil environments. Train-induced vibration is a significant inducement for shallow karst ground collapse. Previous studies on the dynamic properties of surrounding soil under train vibration loads often neglected the impact of time intermittent effects. Taking the red soil covering a typical potential karst collapse area along a high-speed railway in China as the research object, field monitoring of the vibration characteristics of the surrounding environment was conducted. A series of continuous loading and continuous-stop-continuous dynamic triaxial tests and scanning electron microscopy (SEM) tests were designed considering factors such as loading frequency, intermittent duration, and dynamic stress amplitude. The effects of loading intermittence on the dynamic response and microstructure of red soil were compared and analyzed. The experimental results show that the drainage and unloading of red soil samples during the intermittent phase dissipate the accumulated excess pore water pressure and adjust the internal particle and structure of the soil, reducing the accumulation of plastic deformation during subsequent loading stages. The residual strain under vibration loading conditions considering the time intermittent effect is significantly reduced, and the residual strain decreases significantly with the increase of time intervals. The weakening effects of both macro and micro characteristics of red soil in karst-prone areas are significantly enhanced with the increase of intermittent time. The research results are of great significance for the prevention and control of karst ground collapse in karst areas.

An in-deep comprehension of the static and dynamic operational characteristics of prestressed subgrade is essential for its analysis, design, and service performance evaluation. Based on the Buckingham pi theory, a novel scaled static and dynamic model test system of the prestressed subgrade has been developed. The structural components, functional characteristics, and working mechanism of the test system were comprehensively elucidated, and a suite of static and dynamic model tests was conducted to study the deformation characteristics of the prestressed subgrade. It is demonstrated that the prestressed steel bars underwent prestress loss due to the additional stress induced creep of the soil elements below and adjacent to the load transfer plates (LTPs). Therefore, it is advisable to over-tension the prestressed steel bars in practical engineering. Upon the application of prestress, the subgrade surface experienced slight uplift deformation, which did not change the geometric shape and smoothness of the subgrade surface and demonstrated that the prestress reinforcement effect could diffuse to the subgrade surface. In the static double-load-plates tests, the prestressed subgrade presented obvious advantages in controlling the subgrade surface settlement and slope lateral deformation compared to the unreinforced subgrade, which could therefore improve the deformation resistance of the subgrade. In the shortterm dynamic loading tests, both the acceleration and dynamic displacement of the subgrade approximately linearly decreased with an increase in the prestress, implying that the horizontal prestress had a notable beneficial impact on mitigating the subgrade vibration. Additionally, with the long-term dynamic loading, the prestress reinforcements could significantly restrain the cumulative plastic deformation of the subgrade, with the cumulative deformation decreasing as the applied prestress increased. The developed test system offers viable and implementable technical means for investigating the enhancement mechanism of a prestress reinforced subgrade, and the insights gained from the tests contribute to elucidating the effect of prestress reinforcements on the subgrade's static and dynamic performance.

Granular soils exhibit very complex responses when subjected to cyclic loading. Understanding the cyclic behavior of such materials is not only crucial for engineering applications but also the bottleneck of most of constitutive models. This study employs 3D Discrete Element Method (DEM) simulations to explore the accumulative plastic deformation and the internal fabric evolution within granular soils during cyclic loading. Two novel observations are identified: (1) A distinct and unique linear relationship between post-cyclic loading void ratio e and log ( p*/p 0 ) is found independent of the amplitude of cyclic load and the initial stress state prior to cyclic loading, where p* is the mean pressure incorporating cyclic loading stress and p 0 is the mean pressure prior to cyclic loading; (2) When resuming drained triaxial loadings after cyclic loadings, we observe that both microstructural and macroscopic variables converge to the same values they would have reached for pure monotonic drained triaxial loadings. This intriguing behavior underscores and extends to more general loading paths the influential and attractive power of the critical state.

The classical deviatoric hardening models are capable of characterizing the mechanical response of granular materials for a broad range of degrees of compaction. This work finds that it has limitations in accurately predicting the volumetric deformation characteristics under a wide range of con fining/ consolidation pressures. The issue stems from the pressure independent hardening law in the classical deviatoric hardening model. To overcome this problem, we propose a re fined deviatoric hardening model in which a pressure-dependent hardening law is developed based on experimental observations. Comparisons between numerical results and laboratory triaxial tests indicate that the improved model succeeds in capturing the volumetric deformation behavior under various con fining/consolidation pressure conditions for both dense and loose sands. Furthermore, to examine the importance of the improved deviatoric hardening model, it is combined with the bounding surface plasticity theory to investigate the mechanical response of loose sand under complex cyclic loadings and different initial consolidation pressures. It is proved that the proposed pressure-dependent deviatoric hardening law is capable of predicting the volumetric deformation characteristics to a satisfactory degree and plays an important role in the simulation of complex deformations for granular geomaterials. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/ by/4.0/).

The problems of large deformations, failures, and fractures that agricultural tillage tools may encounter during the cultivation process has long been a concern in the field of agricultural machinery design and manufacturing. It is important to establish a more accurate numerical model to effectively predict tools' plastic deformation failures and ductile fracture failures. This research develops a numerical model for predicting the plastic deformation failure and ductile fracture failure of agricultural tillage tools using the smoothed particle hydrodynamics (SPH) method and the Johnson-Cook constitutive model. The model uses the Drucker-Prager criterion to describe the elastic-plastic constitutive behavior of the soil, the von Mises criterion to describe the Johnson-Cook constitutive model of the tool, and the coupling condition with the Lennard-Jones repulsive force to describe the interaction between the tool and soil. The numerical results show that the proposed model can effectively simulate the interaction between the tool and soil, as well as the tool's plastic deformation failure and ductile fracture failure during the agricultural cultivation process. It can also predict the variation trend of the cutting force of the tool. This helps to provide a new approach for the numerical simulation of such problems.

In practical engineering applications, cured lightweight soils are commonly used as roadbed fillers and subjected to intermittent and discontinuous traffic loads. However, previous studies primarily focused on the effects of continuous loading on the mechanical properties of cured soils. To address this knowledge gap, this study investigated the deformation characteristics of fiber-reinforced cured lightweight soils under dry and wet cycles and intermittent loading. Dynamic triaxial tests with varying intermittent ratios and numbers of dry and wet cycles were conducted to assess the influence of these factors on the accumulated plastic strain of fiber-reinforced cured lightweight soils. Based on the test results, a prediction model was developed to estimate the accumulated plastic strain of the cured soils under intermittent loading. The findings indicated that the interval length has a dampening effect on the accumulated plastic deformation of the soil, thereby improving its ability to resist deformation. Additionally, the accumulation of plastic deformation gradually increased with the number of wet and dry cycles but eventually stabilized. In multistage loading, the accumulated plastic strain displayed a rapid increase and stabilization trend similar to that in observed the first loading stage. However, the magnitude of the cyclic dynamic stress ratio determines the deformation at later loading stages. Finally, an improved exponential model was used to establish and validate a prediction model for the cumulative plastic strain of the fiber-reinforced cured lightweight soil under intermittent loading (single and multistage). This prediction model provides important guidance for the practical application of fiber-reinforced cured lightweight soils in engineering projects.