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.

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.

Rainfall-induced debris slides are a major geological hazard in the Himalayan region, where slopes often comprise heterogeneous debris-a complex mixture of rock and soil. The complex nature makes traditional soil or rock testing methods inadequate for assessing such debris's engineering behaviour and failure mechanisms. Alternatively, reduced-scale flume experiments may aid in understanding the failure process of debris slopes. Here, we present findings from reduced-scale laboratory flume experiments performed under varying slope angles (ranging from shallow to steep), initial volumetric water contents (ranging from dry to wet), and rainfall intensities (ranging from light to heavy) using debris materials with a median grain size (D50) 20.7 mm sampled from a rainfall-induced debris slide site in the Himalayas. Hydrological variables, including volumetric water content and matric suction, were monitored using sensors, while slope displacement was tracked indirectly, and rainfall was monitored using rain gauges. The entire failure process was captured via video recording, and index and shear strength tests were performed to characterize the debris material. Our results reveal that the failure of debris slopes is not driven by sudden increases in pore water pressure but by the loss of unsaturated shear strength due to reduced matric suction and a decreased frictional strength from reduced particle contact between grains during rainfall. We also find that the saturation of debris slope by rainfall was quick irrespective of the slope angles and initial moisture contents, revealing the proneness of debris slopes to rainfall-induced failures. These findings provide critical insights into the stability of debris materials and have important implications for improving risk assessment and mitigation strategies for rainfall-induced debris slides in the Himalayas and similar regions worldwide.

Soil-rock mixtures are extensively used in geotechnical engineering applications, such as embankment construction, dam engineering, and slope reinforcement, where their compressive deformation characteristics play a crucial role in influencing the stability and settlement behavior of these structures. This study investigates how variations in rock content (W), effective stress (sigma v) and fine-grained soil properties (quartz sand and silty red clay) affect the one-dimensional compression behavior of soil-rock mixtures. Key compression parameters, including the compression index C c and the secondary compression index C a, were obtained and analyzed through one-dimensional consolidation tests to assess the deformation characteristics of these mixtures. Results show that under the same effective stress (sigma v), both the C c and C a exhibit different trends with W, depending on the properties of the fine-grained soil. Soil-rock mixtures with silty red clay demonstrate more pronounced secondary consolidation effects at low rock content, whereas mixtures with quartz sand display weaker secondary consolidation overall. The significantly lower C a /C c values in the quartz sand mixtures suggest that secondary settlement is much smaller in these mixtures compared to those containing silty red clay.

Colluvial landslides are mainly composed of soil-rock mixtures with complex composition and structure, resulting in large uncertainties in mechanical properties. This leads to difficulties in designing stabilizing piles for colluvial landslides. In this study, we derive a predictive model for the ultimate lateral force of stabilizing piles in soil-rock mixtures, and use it to evaluate the factor of safety of a pile- stabilized colluvial landslide. Subsequently, robust geotechnical design is employed to optimize the design of the stabilizing piles. The design robustness is measured by the variation of failure probability, an approach which can overcome difficulties in characterizing uncertainties in soil-rock mixture mechanical properties. Accordingly, we propose a robust design procedure for stabilizing piles for colluvial landslides. The design method and procedure are illustrated using a real colluvial landslide case study, out of which the most preferred design considering the safety, cost, and design robustness is obtained. Moreover, the influences of rock blocks and safety requirements on the optimal designs are discussed. Our results show that the angle of repose of the rock blocks and the volumetric block proportion determine whether the mechanical parameters of the soil matrix can be used to effectively design the stabilizing pile. It is also found that a higher safety requirement can improve the design robustness, but at higher cost. The advantages of the proposed method are illustrated by a comparison with the traditional reliability-based design method. (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/).

Minimizing the damage caused by landslide disasters in regions with complex geological conditions requires the development of effective and reliable methods for assessing slope stability. This study aims to generate and analyze the stability of random soil-rock mixture slope models, considering the rock block content, spatial distribution, and convexity-concavity feature of rock blocks in the slope. A Python script was developed to create these random soil-rock mixture models using the ABAQUS finite element software. Additionally, the strength reduction technique was applied to calculate the factor of safety via a USDFLD subroutine implemented in ABAQUS. A series of numerical analyses were conducted to assess the impact of rock block content and the convexity-concavity feature of rock blocks on the stability of soil-rock mixture slopes. Moreover, the impact of the random spatial distribution of rock blocks on the stability of soil-rock mixture slopes was discussed. The results show that rock block content below 20% can affect slope stability both negatively and positively. Notably, significant improvements in the stability of soil-rock mixture slopes are observed only when the rock block content exceeds 30%. Furthermore, the convexity-concavity feature of rock blocks can improve the safety factor of the slopes. This study provides a comprehensive methodology and serves as a valuable reference for estimating the safety factor of soil-rock mixture slopes using the finite element method.

Coarse particle shape in slip zone soil influences the mesoscopic structure of the soil, which in turn affects soil shear strength and failure behavior. In order to investigate the effect of particle shape on the shear characteristics of coarse-fine-grained mixed slip zone soil, three types of coarse particles (spheroidal, rounded, and angular) were selected for mixing and matching, and a total of 10 sets of medium-scale shear tests were designed for this paper. To quantify the shear deformation and failure process of slip zone soils, particle image velocimetry (PIV) technology and the hanging hammer method were used to obtain mesoscopic data of the soil (displacement vector data of soil particles and elevation data of the shear failure surface), which were used to calculate shear band thickness, shear dilatation, and roughness coefficient of the shear failure surface. The results indicate that coarse particle shape can considerably affect the macroscopic mechanical properties (internal friction angle and shear strength) and mesoscopic deformation characteristics (shear band thickness, shear dilatation, and shear surface morphology) of soils. Angular coarse particles have higher interlocking strength than spheroidal and rounded coarse particles, allowing angular coarse-grained slip zone soils to develop large shear band thickness and rough shear failure surfaces. In addition, mesoscopic damage analysis suggests that the damage rate of slip zone soils decreases with increasing coarse particle shape complexity. These findings enhance comprehension of the failure characteristics of soil-rock mixture slopes and serve as a good reference for the stability analysis of similar slopes.

To investigate the effects of compaction (K), rock content (RC), and wet-dry cycle (WD) on the road performance of carbonaceous mudstone soil-rock mixtures (CMSRM), orthogonal tests were designed to measure the unconfined compressive strength (UCS) and California bearing ratio (CBR). The correlation degree of K, RC, and WD with the UCS and CBR of CMSRM was investigated using orthogonal theory and grey correlation theory. Based on multivariate nonlinear regression analysis, mathematical models of the road performance of CMSRM were built. The results show that the UCS and CBR of CMSRM were positively correlated with K and negatively correlated with the WD. With increasing RC, UCS increased at first and then decreased, while CBR increased continuously. The failure modes of CMSRM change from tensile failure to shear failure as the K increases under uniaxial compression. The RC and WD affect the structural integrity of the failed samples. Combining the results of range analysis, variance analysis, and grey relational analysis, the most significant influence on the UCS is K, and the most significant influence on the CBR is RC. It is recommended to select 94%-96% for K and 40%-60% for RC in engineering.

For the high-fill slope with soil-rock mixtures (SRMs), the bedrock under the SRMs can be excavated into many benches to improve the mechanical properties of bedrock-SRMs interphase and the stability of the slope. However, this improvement effect by bench size is still unclear. The continuous-discrete coupled method is a powerful tool for analyzing the interaction between soil and structure, soil and rock, etc. Firstly, this paper proposes a fine discrete element modeling method for rock blocks and develops a continuous-discrete coupled method for the benched bedrock-SRMs interphase. Then, a series of numerical direct shear tests for the benched bedrock-SRMs interphases with different bench sizes are conducted. The effect of bench size on the shear mechanical properties of the interphase is systematically investigated in terms of rock block rotation, contact force chain distribution, crack distribution, shear stress-displacement curve, and shear strength. The numerical results demonstrate that the bench size has a considerable impact on the strength and deformation properties of interphase. Raising the height or height-width ratio of the benched bedrock can enhance the interaction and skeletons between the benched bedrock and SRMs, thereby improving the strength and deformation properties of the interphase. Compared to increasing the bench height, increasing the height-width ratio has a more significant effect. Finally, a shear strength prediction method for the benched bedrock-SRMs interphase is proposed based on the Mohr-Coulomb strength criterion, which is practical in the design and stability evaluation of high-fill slope with SRMs. A reverse reconstruction method for building the refined SRMs model is proposed.A coupled FDM-DEM is proposed to simulate the benched bedrock-SRMs interphase.The impacts of bench size on mechanical properties of the interphase are discussed.A shear strength prediction method for the interphase is proposed.