Soil-rock mixtures (SRMs) are characterized by heterogeneous structural features that lead to multiscale mechanical evolution under varying cementation conditions. However, the shear failure mechanisms of cemented SRMs (CSRMs) remain insufficiently explored in existing studies. In this work, a heterogeneous threedimensional (3D) discrete element model (DEM) was developed for CSRMs, with parameters meticulously calibrated to examine the role of matrix-block interfaces under different volumetric block proportions (VBPs). At the macroscopic scale, significant influences of the interface state on the peak strength of CSRMs were observed, whereas the residual strength was found to be largely insensitive to the interface cementation properties. Pronounced dilatancy behaviour was identified in the postpeak and residual phases, with a positive correlation with both interface cementation and VBP. Quantitative particle-scale analyses revealed substantial heterogeneity and anisotropy in the contact force network of CSRMs across different components. A highly welded interface was shown to reduce the number of interface cracks at the peak strength state while increasing the proportion of tensile cracks within the interface zone. Furthermore, the welding degree of the interface was found to govern the formation and morphology of shear cracking surfaces at the peak strength state. Nevertheless, a reconstruction method for the shear slip surface was proposed to demonstrate that, at the same VBP, the primary roughness of the slip surfaces remained consistent and was independent of the interface properties. Based on the extended simulations, the peak strength of the weakly welded CSRMs progressively decreased with increasing VBP, whereas further exploration of the enhanced residual strength is needed.

During the excavation of large-scale rock slopes and deep hard rock engineering, the induced rapid unloading serves as the primary cause of rock mass deformation and failure. The essence of this phenomenon lies in the opening-shear failure process triggered by the normal stress unloading of fractured rock mass. In this study, we focus on local-scale rock fracture and conduct direct shear tests under different normal stress unloading rates on five types of non-persistent fractured hard rocks. The aim is to analyze the influence of normal stress unloading rates on the failure modes and shear mechanical characteristics of non-persistent fractured rocks. The results indicate that the normal unloading displacement decreases gradually with increasing normal stress unloading rate, while the influence of normal stress unloading rate on shear displacement is not significant. As the normal stress unloading rate increases, the rocks brittle failure process accelerates, and the degree of rocks damage decreases. Analysis of the stress state on rock fracture surfaces reveals that increasing the normal stress unloading rate enhances the compressive stress on rocks, leading to a transition in the failure mode from shear failure to tensile failure. A negative exponential strength formula was proposed, which effectively fits the relationship between failure normal stress and normal stress unloading rate. The findings enrich the theoretical foundation of unloading rock mechanics and provide theoretical support for disasters prevention and control in rock engineering excavations. (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/).

In order to explore the rules for the variation in the adfreeze shear strength at the interface between frozen soil and a pile foundation, and their influencing factors, a measuring system was developed to estimate the freezing strength at the interface by utilizing a pile-pressing method under a cryogenic environment. Experimental results demonstrate that the maximum vertical pressure on the pile top increased significantly with the decrease in temperature under the same moisture content. The shear stress-shear displacement curves, at the bottom part of the interface, presented strain-softening characteristics, while the strain-hardening phenomenon was observed at the upper part of the interface. The strength parameters of the interface decreased with the increase in the pile depth. Moreover, the influence of temperature on the shear strength of the interface was more significant compared with that of the moisture content. The research results can provide references for the construction of pile foundations, structural design optimization, and for frozen damage prevention and treatment in permafrost regions.

Understanding the shear mechanical behaviors and instability mechanisms of rock joints under dynamic loading remains a complex challenge. This research conducts a series of direct shear tests on real rock joints subjected to cyclic normal loads to assess the influence of dynamic normal loading amplitude (Fd), dynamic normal loading frequency (fv), initial normal loading (Fs), and the joint roughness coefficient (JRC) on the mechanical properties and instability responses of these joints. The results show that unstable sliding is often accompanied by friction weakening due to dynamic normal loads. A significant negative correlation exists between cyclic normal loads and the normal displacement during the shearing process. Dynamic normal load paths vary the contact states of asperities on the rough joint surfaces, impacting the stick-slip instability mechanism of the joints, which in turn affects both the magnitude and location of the stress drop during the stick-slip events, particularly during the unloading phases. An increasing Fd results in a more stable shearing behavior and a reduction in the amplitude of stick-slip stress drops. The variation in fv influences the amplitude of stress drop for the joints during shear, characterized by an initial decrease (fv = 0.25-2 Hz) before exhibiting an increment (fv = 2-4 Hz). As Fs increases, sudden failures of the interlocked rough surfaces are more prone to occur, thus producing enhanced instability and a more substantial stress drop. Additionally, a larger JRC intensifies the instability of the joints, which would induce a more pronounced decline in the stick-slip stress. The Rate and state friction (RSF) law can provide an effective explanation for the unstable sliding phenomena of joints during the oscillations of normal loads. The findings may provide certain useful references for a deeper comprehension of the sliding behaviors exhibited by rock joints when subjected to cyclic dynamic disturbances. (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/).

The deterioration of shear resistance in rock and soil masses has resulted in numerous severe natural disasters, highlighting the significance of long-term monitoring for disaster prevention and mitigation. This study explores the use of a nondestructive method to quickly and accurately evaluate the shear properties of soil-rock mixture. The shear stress, shear strain, and resistivity of the soil-rock mixture were tested simultaneously using a combination of direct shear and resistivity tests. The test results show that the resistivity of the soil-rock mixture gradually decreases with increasing shear strain. The resistivity of all specimens ranged approximately from 60 to 130 Omega.m throughout the shear process. At the end of the shear test, the vertical failure resistivity showed an irregular W shape with increasing rock content. It exhibited a significant negative linear functional relationship with the shear strength. With reference to the determination of cohesion and internal friction angle on the shear strength envelope, the horizontal angle of the vertical failure resistivity-normal stress curve is defined as the resistivity angle, and the intercept of the curve is the resistivity at the initial moment of shear. It has been observed that the resistivity angle is negatively and linearly correlated with the internal friction angle. At the same time, there is a linear growth relationship between resistivity at the initial moment of shear and cohesion. It has been demonstrated that an increase in rock content contributes to a general escalation in both the average structure factor and average shape factor. Meanwhile, a decrease in the anisotropy coefficient has also been noted. These alterations are indicative of the extent of microstructural transformations occurring during the deformation process of the soil-rock mixture. The research results verify the feasibility of real-time deformation monitoring and characterization of shear strength parameters using resistivity.

Using geotextiles to improve saline soil roadbeds has become increasingly widespread. However, salt unavoidably enriches at the saline soil-geotextile interface. Under complex external forces, the mechanical properties of the saline soil geotextile interface are not yet clear. Therefore, this study systematically studied the dynamic shear performance of saline soil geotextile interface under dynamic load under different salt content conditions using three shear forms: cyclic direct shear, monotonic direct shear, and post-cycle direct shear. The main research focuses on the influence of salt content, vertical stress and shear displacement amplitude on interface shear strength, stiffness, damping ratio, vertical displacement and other indicators. The results show that after cyclic shear, the strength of the interface of saline soil decreases, and the phenomenon of plastic softening is obvious. The interface shear strength and stiffness exhibit a non-linear relationship with the increase of salt content. When the salt content is 3 %, the interface shear performance reaches its optimum. Excessive salt content can cause crystalline slippage and weaken interface mechanical properties. Increasing vertical stress or reducing shear displacement amplitude is beneficial for improving interface shear strength and stiffness. The amplitude of shear displacement has the greatest impact on the interface damping ratio. The higher the salt content, the more severe the stress damage to the geotextile, and the more significant the accumulation of interface crystallization. The study revealed the mechanical response law of saline soil geotextile interface under dynamic load.

In regions with seasonal frozen soil, mechanical properties of soil are impacted by freeze-thaw cycles, which influence the shear resistance of soil-concrete interface in geotechnical engineering. For evaluating shear properties at the soil-concrete interface, freeze-thaw cycles and direct shear experiments were conducted in this research. The stress-displacement curves, shear strength and parameters of the interface were analyzed in relation to freeze-thaw cycles, while the influences by moisture contents and normal stresses were considered. Results show that the curves related to shear stresses and displacements at the interface are strain-hardening, and shear properties gradually deteriorate with repetitive freezing and thawing. The shear strength is positively related to normal stresses, and it increases by approximately 250% while normal stress varies from 100 to 400 kPa. However, it is negatively correlated with growing moisture contents and freeze-thaw cycles. The reduction in shear strength is about 21%-25% after freeze-thaw cycles, along with a decrease in cohesion ranging from 14% to 20% and for angle of internal friction it reaches at 14%-24%. Moreover, an improved hyperbolic model based on the logistic function and hyperbolic model was established to evaluate shear properties at the interface under freeze-thaw cycles, providing a theory base for engineering construction in seasonally frozen soil regions.