Mechanical Properties Of Soil Rock Mixture Under Seepage Macroscopic And Microscopic Studies

Soil-rock mixtures are widely distributed in China,especially in the western region.Along with the advancement of various large hydropower projects,soil-rock mixtures have gradually received the attention of geotechnical researchers.The soil-rock mixture is a complex soil body,composed of two materials（rock and soil）with different properties,and has strong inhomogeneity and discontinuity,and its macroscopic mechanical properties are closely related to the boulder content,shape and other fine structural characteristics.When soil-rock mixtures are used as hydraulic materials in various hydraulic projects（e.g.earth and rock dams）,the influence of seepage on them cannot be ignored.This article focuses on the mechanical properties of soil-rock mixtures,taking into account factors such as rock content,block shape,seepage pressure,and confining pressure.Three methods of research are used:indoor triaxial testing,numerical image modeling,and biaxial compression and seepage pressure testing with random block placement.The main work of this article is as follows:（1）Systematically summarize the current research status of soil-rock mixtures and analyze the main problems existing in them.On this basis,the research contents and methods of this paper are proposed,and the main technical route and implementation plan of the research on the mechanical properties of soil-rock mixtures are determined.（2）The basic physical tests are conducted on the remodeled soil-rock mixture to obtain the physical indexes of the soil sample;the indoor triaxial tests are carried out to study the effects of stone content rate and surrounding pressure factors on the macroscopic mechanical properties of the soil-rock mixture.（3）The image processing technology is used to pre-process the numerical image of the soil-rock mixture,obtain its binarized numerical image,extract the block boundary information,and import it into PFC^2D software for particle filling to generate the block clump model,and build a soil-rock mixture model considering the real block shape,based on which a flexible biaxial test is conducted and compared with the indoor triaxial test results to obtain The simulation results are in good agreement with the indoor test results.（4）The PFC random block placement code was compiled to construct a random soil-rock mixture model,and the parameters were calibrated based on the relationship between macroscopic parameters.The same flexible biaxial numerical tests were conducted on the specimens to study the influence of stone content and surrounding pressure on the stress-strain curve,strength characteristics and deformation-damage characteristics of the soil-rock mixture,and further analyze the fine mechanical response such as the change of inter-particle contact force and particle motion law.The results show that the mechanical properties of the soil-rock mixture have obvious zoning,and the mechanical properties of the soil samples are jointly determined by the soil and the boulders in the range of 25%～55%of the stone content,and when the stone content is greater than 55%,the properties are mainly determined by the boulders.（5）Two modules of fluid and mechanical calculations are carried out for the soil-rock mixture,and the mechanical properties of the soil-rock mixture are studied.The influence of seepage flow is considered on the basis of biaxial compression,and parameters such as seepage velocity and permeability coefficient of the specimen are monitored and calculated to explore the influence of stone content and seepage pressure on the mechanical properties and permeability of the soil-rock mixture,and the permeability of the soil-rock mixture is obtained to grow nonlinearly with the stone content and increase with the seepage pressure The permeability of the soil-rock mixture increases non-linearly with the stone content and increases with the increase of seepage pressure.The peak strength in the stress-strain relationship decreases with increasing seepage pressure,and the gravel content mainly affects the post-peak curve at the same permeability pressure.