Soil-rock mixtures are composed of a complex heterogeneous medium, and its mechanical properties and mechanism of failure are intermediate between those of soil and rock, which are difficult to determine. To consider the influence of different particle groups on soil-rock mixture's shear strengths, based on the mesomotion properties of the particles of different particle groups when the soil-rock mixture is deformed, it is classified into two-phase composites, matrix and rock mass. In this paper, based on the representative volume element model of soil-rock mixtures and the Eshelby-Mori-Tanaka equivalent contained mean stress principle, a model of shear constitutive of the accumulation considering the mesoscopic characteristics of the rock is established, the influence of different factors on the shear strength of the accumulation is investigated, and the mesoscopic strengthening mechanism of the rock on the shear strength of the accumulation is discussed. The results show that there is a positive correlation between the rock content, the surface roughness of the rock, the stress concentration coefficient, coefficient of average shear displacement, and the accumulation's shear strength. When the accumulation is deformed, it stores or releases additional energy than the pure soil material, so it shows an increase in deformation resistance and shear strength on a macroscopic scale.

The mechanical properties and failure characteristics of soil-rock mixtures (SRMs) directly affect the stability of tunnels constructed in SRMs. A new SRM modelling method based on the combined finite-discrete element method (FDEM) was proposed. Using this new SRM modelling method based on the FDEM, the mechanical characteristics and failure behaviour of SRM samples under uniaxial compression, as well as the failure mechanism of SRMs around a tunnel, were further investigated. The study results support the following findings: (1) The modelling of SRM samples can be achieved using a heterogeneous rock modelling method based on the Weibull distribution. By adjusting the relevant parameters, such as the soil-rock boundaries, element sizes and modelling control points, SRM models with different rock contents and morphologies can be obtained. (2) The simulation results of uniaxial compression tests of SRM samples with different element sizes and morphologies validate the reliability and robustness of the new modelling method. In addition, with increasing rock content, VBP (volumetric block proportion), the uniaxial compressive strength and Young's modulus increase exponentially, but the samples all undergo single shear failure within the soil or along the soil-rock interfaces, and the shear failure angles are all close to the theoretical values. (3) Tunnels in SRMs with different rock contents all exhibit X-shaped conjugate shear failure, but the fracture network propagation depth, the maximum displacement around the tunnel, and the failure degree of the tunnel in the SRM roughly decreases via a power function as the rock content increases. In addition, as the rock content increases, such as when VBP = 40%, large rocks have a significant blocking effect on fracture propagation, resulting in an asymmetric fracture network around the tunnel. (4) The comparisons of uniaxial compression and tunnel excavation simulation results with previous theoretical results, laboratory test results, and numerical simulation results verify the correctness of the new modelling method proposed in this paper.

Red stratum is widely distributed in Southwest China, and a large number of deep soil-red stratum soft rock mixed backfill areas were formed when the site was leveled by high excavation and low filling during the construction of mountain city in this area. Tunnels under construction inevitably go through backfill, which makes tunnel excavation under deep soil-rock mixture backfill become a common condition. Meanwhile, rainfall is frequent and concentrated in Southwest China, and the resulting wet disintegration of red stratum soft rock has a significant impact on the deformation and bearing characteristics of soil-rock mixture. As a result, it was decided in the present study to conduct a shear-unloading test on the soil-red stratum soft rock mixture, augmented by discrete element numerical simulations, to reveal the influence of wetting. This all-encompassing strategy seeks to examine the laws governing the deformation and progression of damage of the mixture, offering valuable insights into its response when subjected to unloading conditions. The findings indicate that the soil-red stratum soft rock mixture prior to and after wetting shows obvious strain hardening characteristics during the shear process. The residual strength after unloading has a linear correlation with unloading amplitude. The soilred stratum soft rock mixture prior to wetting is loaded by the rock block bearing skeleton, and the rock block breakage is primarily caused by shear, while jointly loaded by soil and rock block in saturated sample, with the rock block breakage caused by wetting. After the unloading process, the dry sample's bearing capacity no longer increases and eventually overall failure occurs. Conversely, the saturated sample's bearing capacity can continue to increase and ultimately layered failure from the top to the bottom occurs. The unloading rate mainly affects the growth rate of load-bearing capacity after unloading of saturated samples.

Purpose - The purpose of this paper is to propose a new combined finite-discrete element method (FDEM) to analyze the mechanical properties, failure behavior and slope stability of soil rock mixtures (SRM), in which the rocks within the SRM model have shape randomness, size randomness and spatial distribution randomness. Design/methodology/approach - Based on the modeling method of heterogeneous rocks, the SRM numerical model can be built and by adjusting the boundary between soil and rock, an SRM numerical model with any rock content can be obtained. The reliability and robustness of the new modeling method can be verified by uniaxial compression simulation. In addition, this paper investigates the effects of rock topology, rock content, slope height and slope inclination on the stability of SRM slopes. Findings - Investigations of the influences of rock content, slope height and slope inclination of SRM slopes showed that the slope height had little effect on the failure mode. The influences of rock content and slope inclination on the slope failure mode were significant. With increasing rock content and slope dip angle, SRM slopes gradually transitioned from a single shear failure mode to a multi-shear fracture failure mode, and shear fractures showed irregular and bifurcated characteristics in which the cut-off values of rock content and slope inclination were 20% and 80 degrees, respectively. Originality/value - This paper proposed a new modeling method for SRMs based on FDEM, with rocks having random shapes, sizes and spatial distributions.

The red stratum soft rock, contained extensively in the deep soil-rock mixture (SRM) backfill area of southwest China, exhibits significant water-disintegrating properties that greatly impact the foundation's bearing capacity and deformation failure in this region. This study introduced the large-scale triaxial test to investigate the mechanical deformation characteristics of clay-red stratum soft rock mixture before and after wetting. Simultaneous, combined with the results of test, the law of water disintegration of red stratum soft rock was revealed, and its effects were analyzed in detail. The results show that: (1) Wetting intensified the crushing of rock blocks, resulting in the reduction of shear strength and critical strain of the samples, the decrease of critical internal friction angle and secant modulus, and the significant increase of the relative crushing rate of rock blocks; (2) The most significant increase and decrease of the content before and after the test occur in the particles with the particle size of 0.5-2 mm and 20-40 mm, respectively; (3) Wetting-induced breakage of the red stratum soft rock mainly occurs during the first two hours after encountering water; (4) An increase in confining pressure exacerbates the influence of wetting. Additionally, based on the theory of non-linear elasticity, with the assuming that the reduction of secant modulus causes the wetting deformation, a theoretical calculation model of the wetting axial strain was proposed. Through comparing the calculated results with the measured values obtained by using the double-line method and single-line method test, it is found that the calculation method can accurately predict the wetting axial strain of SRM and be used for quantitative analysis of wetting deformation.

The variation of ultrasonic parameters is closely linked to the mechanical properties and damage evolution of rock and soil mass. In this paper, uniaxial compression tests and real-time ultrasonic monitoring technology were used to explore the strength, deformation and damage characteristics of frozen soil-rock mixture (FSRM) with different block sizes and gradations, as well as the law of ultrasonic wave propagation. The results indicate that: (1) A wider gradation of rock blocks corresponds to a higher specimen strength and a lower breakage degree of rock blocks. Within the same gradation, specimens with smaller block sizes have higher strength. Wider gradation and smaller particle size of rock blocks exerts a delayed effect on damage and failure of FSRM. (2) The particle size of rock blocks plays a key role in the variation of ultrasonic parameters. Within the same gradation, the specimens with larger block sizes possess higher wave velocity and lower first wave amplitude. The effect of gradation on ultrasonic parameters is attributed to the variation of block size. (3) With the first wave amplitude as damage state variable, a damage prediction model based on the improved Duncan-Chang model is established, demonstrating superior prediction potential on the stress-strain curves of FSRM. The research confirms and promotes the quantitative correlation between ultrasonic parameters and mechanical properties of geotechnical materials, which may provide theoretical support for testing and evaluating the mechanical properties of roadbed filling in cold mountainous areas.

This study adopts the Smoothed Particle Hydrodynamics (SPH) technique to accurately and efficiently replicate and forecast the mesoscopic behavior of soil-rock mixtures (SRM). It introduces a novel approach for generating rock blocks within the SRM, utilizing a method that randomly selects angles and lengths. In addition, this research proposes a method for discretizing any shaped region into free particles with specific material attributes, named the regional medium particle discretization method. It incorporates the Drucker-Prager constitutive model to develop the SPH numerical model for SRM. Furthermore, it examines the effects of different rock sizes and rock contents on the SRM's failure characteristics and mechanical properties. The findings revealed that, for identical rock contents, smaller rock samples exhibit a more dispersed failure surface with numerous secondary shear bands, whereas larger rock samples display a smoother and more concentrated failure surface. As the rock content decreases, shear bands typically form in the sample's center and are relatively straight. However, as the rock content increases, the shear bands' configuration becomes more intricate, often featuring multiple shear bands. This method offers a fresh perspective for exploring the mechanical properties of heterogeneous materials.

The strength deterioration of soil-rock mixtures (SRM) subjected to freeze-thaw (F-T) cycles leads to instability and failure of upper engineering structures in cold regions. However, the mutual feedback response mechanism pertaining to the changes of pore and strength in SRM under F-T cycles are rarely addressed. Nuclear magnetic resonance and triaxial tests were carried out to study the pore structure characteristics and strength response patterns of samples. A correlation model of SRM porosity and strength deterioration was first proposed under F-T cycles, and the model rationality was verified by test data. The results demonstrated that the pore connectivity and porosity increased throughout the F-T process, with the T2 spectral distribution curves exhibiting three peaks. Among these peaks, the main peaks underwent slight changes, while the secondary and micro peaks presented significant changes. Before 3 F-T cycles, the pore distribution evolved to small pores uniformly, followed with the large pores increasing and the micropores disappearing. With increasing of F-T times, the strength and cohesion of SRM experienced a drastic decline, while the internal friction angle demonstrated a slight decrease accompanied by fluctuations. Based on the analysis of test results, a correlation model regarding the porosity and strength deterioration was proposed through the relationship between the micro-structure evolution and the macro-mechanical response during F-T cycles. Furthermore, intrinsic mechanism of SRM strength deterioration under F-T cycles was revealed by considering the pore structure characteristics. The results can provide theoretical insights for the analysis of F-T disaster mechanism and prevention of SRM in cold regions.

Stability issues and the resulting economic and human losses associated with soil-rock mixture slopes (SRMS) are significant concerns. To address these stability problems in SRMS, h-type anti-slide piles (hTP) have been recognized as reliable stabilizing structures. This research involves a series of five centrifuge model tests conducted to investigate the stress response of hTPs under various pile parameter scenarios. The experiments were designed to evaluate the impact of variables such as pile spacing, anchoring depth, and beam rigidity, leading to practical recommendations for the effective use of hTPs. Centrifuge tests unveiled that the rear pile undergoes an M-shaped bending moment distribution, marked by three crucial inflection points situated approximately at 1/4 h(2),4/7 h(2), and 5/6 h(2). In contrast, the front pile exhibits a V-shaped bending moment distribution, reaching its peak at a depth of 6/7 h(1). The alteration of the bending moment throughout the loading phases is divided into three distinct periods: the slow creep stage, the slow growth stage, and the rapid growth stage. Moreover, it was noted that the bending moment of hTP intensifies with an increase in pile spacing, while the depth of anchoring shows no significant influence on the magnitude of the bending moment.

新疆天山北坡山区流域水文气象资料稀缺，融雪径流模拟比较困难。为研究HBV模型在新疆天山北坡玛纳斯河流域径流模拟的适用性，通过分析流域积雪覆盖率与径流的相关性，并基于中国地面降水与气温日值0.5°×0.5°格点数据集，经空间插值得到研究区多年平均降水和气温的空间分布，运用HBV模型模拟了玛纳斯河流域2000—2013年日尺度和月尺度径流过程，与SRM的模拟效果进行对比分析。结果表明：（1）多年月平均积雪覆盖率与多年月平均流量呈负相关，相关系数R2=0.67,流域内积雪融水对径流的补给作用明显；（2）数据集经空间插值得到研究区多年平均降水和气温的空间分布能基本反映流域的垂直气候差异性，数据集可作为玛纳斯河流域缺乏气象资料的高山区径流模拟的输入数据；（3）HBV模型与SRM在玛纳斯河流域日尺度和月尺度的径流模拟效果评价等级均为良好，且HBV模型对洪峰流量模拟效果更好，整体的模拟值与实测值偏差更小，HBV模型在玛纳斯河流域具有较好的适用性。