Mechanical Properties And Damage Evolution Mechanism Of Anchored Layered Shale In Tension-shear Fracture

Correspondingly,in practical engineering,the failure modes of rock are often divided into three types:tension failure,compression shear composite failure,and tension shear composite failure.It is generally accepted that tensile stress exists in rock slopes.At the same time,considering that jointed rock mass exists widely in nature,weak bedding has a great influence on the strength and stability of rock,and tension shear composite failure occurs mostly in layered rock mass,indicating that it is of great significance to study the mechanism of anchoring jointed rock mass under tension shear stress.In this thesis,the self-designed tension shear auxiliary device is used to design the tension shear test of anchored rock mass under different normal stress conditions.At the same time,acoustic emission technology was used to study the mechanical characteristics and damage evolution mechanism of rock tension shear fracture,and compared with the compression shear test results.The main research results are as follows:（1）The tension shear tests were carried out by self-designed tension shear auxiliary devices,and the deformation,strength,fracture surface and other properties of anchoring rock mass were obtained,and the composite mechanism of tension shear between rock mass and anchor bolt was analyzed.The test analysis shows that the tension shear device can carry out the tension shear test well.The peak strength is more sensitive to normal tension,and Hoek-Brown yield criterion can generally characterize the strength characteristics of the full stress area.Tension shear samples separated quickly after peak,and the brittle characteristics were significant compared with compression shear samples wave after peak.The anchored tension shear rock sample undergoes two yields of the rock and the bolt,and the damage jumps several times.After the peak,the residual stress is only provided by the tensile and shearing of the bolt.（2）The morphological characteristics of the rock fracture surface are closely related to the direction and magnitude of the normal stress.The fractal dimension D and the roughness coefficient R_s have a positive correlation with the normal stress,and the roughness and fracture degree of the fracture surface in normal tension are smaller than those in normal compression.The microcracks in the compression shear rock sample expand in multiple directions,resulting in shear fractures along or through the bedding.The damage curve is"S"shaped,which is ductile failure.The microcracks in the tension shear rock sample extend along the bedding plane,resulting in intergranular fracture along the bedding,and the curve is"J"shaped,which is brittle failure.The wear degree of the fracture surface of the anchored tension shear rock sample is reduced,the shear fracture zone at the fracture is obviously weakened,the curve is a composite state of"J"shape and"S"shape,and the failure mode changes from"brittleness"to"ductility".（3）Based on parameters such as rock damage degree and evolution law represented by acoustic emission signal and its derived parameters,the rock damage evolution is divided into different stages,and a model to quantify rock damage is deduced,and a precursor prediction index of rock damage is proposed.The analysis results show that the damage is slight in the initial stage of tension shear and compression shear tests,which belongs to the calm period of AE signal,and the duration of AE signal increases with the normal stress.The time required for each stage of tension shear test curve is shorter and the rate of damage is faster.The damage degree represented by acoustic emission parameters of tension shear samples is smaller than that of compression shear samples.The normalized damage of tension shear curves changes from monotonically increasing and the growth rate increases continuously to stepped growth and the growth rate of peak stress point tends to zero before and after anchoring.（4）The damage model can describe the evolution of rock damage degree with time in the tension and compression full stress region.The AE b fluctuates in a certain range before rock failure and continues to decrease when rock failure occurs.The critical point of the stress-displacement curve?_cd and the several slowly decreasing segments of the dissipated energy U_d before the peak of the deformation curve can be used together as a precursory early warning of rock failure.At the same time,the critical points?_cc,?_ci and?_cd of shear stress at each stage are consistent with the rock damage process characterized by AE parameters,which can comprehensively evaluate the damage evolution mechanism of rocks from two aspects of macroscopic stress change and microscopic crack propagation evolution.