In the construction of cold region engineering and artificial freezing engineering, soil-rock mixture (SRM) is a frequently encountered geomaterial. Understanding the mechanical properties of frozen SRM is crucial for ensuring construction safety. In this paper, frozen SRM is considered as a multiphase material consisting of a soil matrix and rock. By employing a single-variable approach, the relationship between UCS and rock content was revealed, and the effects of rock content on the stress-strain curve shape and failure mode were analyzed. The test results indicate that rock content significantly influences the stress-strain curve and failure mode of SRM. The specimen preparation with different rock content is unified using a given relative compactness. The uniaxial compressive strength (UCS) of the frozen specimens increases firstly and then decreases as rock content increases, which is unaffected by temperature or rock size. The classic quadratic polynomial is suggested to describe the variation rule. The failure modes of specimens with low, medium and high rock content correspond to shear failure, bulge failure and splitting failures, respectively, which transmits from shear failure to splitting failure as the rock content increases.

This investigation focused on the cementation mechanisms and mechanical properties of soil-rock mixtures-slurry cement (SRM-SC) to ensure the safety of tunnels during operation. SRM-SC specimens were prepared with different types of slurry and rock contents based on an actual slurry injection ratio. The macroscopic level analysis involved measuring the specimens' uniaxial compressive strength and shear strength, determining the strength parameters, and analyzing the damage forms. At the microscopic level, the surface morphology and composition of the specimens were examined using scanning electron microscope imaging. This allowed for a comparative analysis of the cementation ability and mechanism of the slurry under different control conditions, providing a basis for determining the mechanical properties of SRM-SC. The results indicated that the rock content significantly impacts the macromechanical properties of SRM-SC. The compressive strength and stiffness of SRM-SC initially increase and then decrease with the increasing rock content, with an inflection point observed between a 20% and 60% rock content. On the other hand, the shear strength and stiffness both increase with the increasing rock content. Additionally, the macroscopic mechanical properties of SRM-SC formed by different types of grout exhibit noticeable differences. These findings serve as a reference for regulating the mechanical properties of SRM-SC.

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.

Soil-rock mixture is a typical two-phase composite material. The physicomechanical properties and relative quantities of each component greatly influence the macroscopic mechanical properties of the soil-rock mixture. This study takes the macroscopic and mesoscopic coupling perspective and uses the discrete element direct shear test as the main method to comprehensively investigate the effects of rock content and rock particle size on the mechanical properties of the soil-rock mixture. The results show that the macroscopic shear strength of soil-rock mixture specimens increases with the increase of rock content. The initial packing state and compactness of specimens affect their shear dilation performance to some extent. The contact force chain distributions within specimens under different soil-rock combinations differ significantly. However, a very obvious force chain band is observed in the specimens at the end of the shearing (ranging from the upper left of the shearing box to its lower right). The contact force branch vectors within the force chain band are thick and dense, with obvious directionality (all from top left to bottom right). Under the same vertical load, the average coordination number of particles on the shear surface decreases with the increase of rock content. Within the same specimen, the average coordination number of particles on the shear surface increases with the increase of vertical load.

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.

In cold regions, the strength of soil-rock mixture (SRM) is gradually reduced by freeze-thaw (F-T) cycles, in order to study the deterioration mechanism of mechanical properties of SRM under F-T cycles, indoor triaxial tests were carried out by taking into account the effects of the number of F-T cycles, the rock content and the confining pressure, and combined with the numerical simulation of particle discrete elements to analyze the microscopic deformation of the failure characteristics of the SRM, as well as the development law of the shear surfaces and the contact force chain. The results showed that the F-T cycle did not have much effect on the stress-strain curve morphology, but the peak and initial slope of the stress-strain curve increased with the increase of the rock content. The F-T cycle has a more obvious deterioration effect on the failure strength, elastic modulus and cohesion of the samples, but has less effect on the internal friction angle. The failure strength and elastic modulus of the samples increased with the increase of the confining pressure. With the increase of rock content, the failure strength, elastic modulus and internal friction angle of the samples increased, but the cohesion decreased. Under the flexible loading condition, the SRM samples exhibit swell failure, and the shear zone formed after failure is roughly distributed in an X shape, and the failure morphology of the SRM samples, as well as the morphology and size of the shear zone, are all affected by the rock content and the confining pressure. The contact force between particles in the SRM samples increases with the increase of rock content, and the chain of coarse force is mainly distributed in the vicinity of rock particles, but the F-T cycle will weaken the contact force between particles, thus reducing the strength of the SRM.

Fault fracture zones, characterized by high weathering, low strength, and a high degree of fragmentation, are common adverse geological phenomena encountered in tunneling projects. This paper performed a series of large-scale triaxial compression tests on the cohesive soil-rock mixture (SRM) samples with dimensions of 500 mm x 1000 mm to investigate the influence of rock content P-BV (20, 40, and 60% by volume), rock orientation angle alpha, and confining pressure on their macro-mechanical properties. Furthermore, a triaxial numerical model, which takes into account P-BV and alpha, was constructed by means of PFC3D to investigate the evolution of the mechanical properties of the cohesive SRM. The results indicated that (1) the influence of the alpha is significant at high confining pressures. For the sample with an alpha of 0 degrees, shear failure was inhibited, and the rock blocks tended to break more easily, while the samples with an alpha of 30 degrees and 60 degrees exhibited fewer fragmentations. (2) P-BV significantly affected the shear behaviors of the cohesive SRM. The peak deviatoric stress of the sample with an alpha of 0 degrees was minimized at lower P-BV (60%). Based on these findings, an equation correlating shear strength and P-BV was proposed under consistent alpha and matrix strength conditions. This equation effectively predicts the shear strength of the cohesive SRM with different P-BV values.

Due to the considerable variation in the range of rock content of the soil-rock mixture, when grouting experiments were conducted according to the existing grouting theory, it was found that a large number of pores not entirely filled by the slurry existed in the concretions of the medium to high rock content backfill area. Therefore, the existing slurry permeation grouting diffusion equation was optimized by adding the filling factor (gamma). Based on the Bingham fluid rheological equation and the Newtonian fluid rheological equation, the optimized calculation equations for Bingham fluid and Newtonian fluid permeation diffusion considering the filling factor (gamma) were derived. Furthermore, the indoor grouting experiment data are compared and analyzed with the calculation results of the original formula and the optimized formula. The results show that when ignoring the unfilled pores, the original formula calculating the diffusion radius will be small; the calculation results of the optimized formula considering the filling factor (gamma) are closer to the actual experiment results. Moreover, based on the calculation results of the optimized formula, the order of influencing factors of the permeation diffusion radius is rock content > void ratio > water-cement ratio > grouting pressure.