Study On Shear Characteristics Of Mud Sandstone Anisotropic Discontinuity Based On Particle Flow

The shear strength of rock mass discontinuities is an important factor affecting the stability of rock mass.In nature,there are widely heterogeneous discontinuities with different lithologies on both sides.Therefore,the study of the deformation and strength characteristics of heterosexual discontinuity is to provide a basis for the stability evaluation of rock mass.This paper takes the Jurassic mud-sandstone interbedded rock in the Three Gorges reservoir area as the research object.Based on the combination of laboratory test and numerical simulation test,the shear strength characteristics,size effects and meso mechanism of failure process of discontinuities are studied based on Barton's ten standard profile lines.Finally,a new type of shear strength criterion for heterogeneous rock mass structural planes is proposed on the basis of the Barton criterion.The main research contents and conclusions of this paper are as follows:(1)Firstly,the direct shear test of sandstone is carried out in laboratory,and the shear strength values of sandstone under different normal stresses are obtained.For mudstone,the shear strength parameters of mudstone are obtained according to the existing test data.Secondly,a numerical simulation test of particle flow on a mud-sandstone heterogeneous discontinuity is established,and the micro parameters are calibrated by combining the macro parameters obtained by the laboratory test.(2)Different normal stresses are applied to the structural surfaces of heterogeneous rock masses with different roughness.The study found that as the normal stress increases,the shear strength of the structural surfaces also increases.Under the same normal stress,as the roughness increases,the shear strength of the structural surface also increases.It can be concluded that the normal stress and roughness are the main factors affecting the shear strength of the structural surface.By setting 4 different sizes,the relationship between the shear strength and size of the heterogeneous structural plane is studied.The study found that as the size of the structural plane increases,the shear strength of the structural plane gradually decreases,indicating that the shear strength of the structural plane has a size effect.(3)Analyze the acoustic emission characteristics of the heterogeneous structural surface.There is no acoustic emission at the beginning of loading;a small number of stable acoustic emission phenomenon appears before the peak value;when the peak intensity is reached,the acoustic emission quantity increases suddenly and is the largest acoustic emission in the shear process;in the failure stage,a large amount of acoustic emission will appear at each stress drop;in the residual intensity stage,the acoustic emission event continues to occur steadily.(4)Analyze the crack characteristics of the heterogeneous discontinuities.There are a small number of cracks before the peak.After reaching the peak strength,the cracks begin to generate,expand and penetrate.The number of cracks rises vertically.In the residual strength stage,under the action of normal stress Cracks continue to occur,showing a slow and steady growth trend.(5)The cracks gradually extend from one end to the other.In addition to the main cracks on the mud-sandstone interface,there are also multiple secondary cracks on the side of the mudstone with lower strength.With the increase of structural surface roughness,the degree of structural surface undulation has a great effect on the development direction of cracks.The main crack will develop along the direction of structural surface undulation,and gradually incline to the mudstone side.(6)The Barton JRC-JCS criterion is used to compare and analyze the shear strength of heterogeneous discontinuities and homogeneous discontinuities.The study found that the shear strength of heterogeneous discontinuities is between that of sandstone and mudstone discontinuities of the same sex.After analyzing the failure mechanism of homogeneous discontinuities,the Barton strength criterion applicable to the structural plane of heterogeneous discontinuities is proposed by introducing a new parameter.Under low stress,the shear strength of the structural plane is close to the shear strength of mudstone,and under high normal stress,the shear strength of the structural plane is close to the shear strength of sandstone.