Research On The Shear Mechanical And Rheological Properties Of Peretrating Jointed Rock Mass Under Unloading Normal Stress

The compression-shear damage of rock masses along the structural surface is one of the most common damage methods in practical engineering,and the shear mechanical properties and deformation characteristics of the structural surface of rock masses have been an important scientific problem studied in the fields of engineering geology and rock mechanics at home and abroad.The current experimental research on the shear mechanical properties of the structural surface mainly adopts the loading method of increasing shear stress by constant normal stress,while in practice the excavation of the rock mass mostly shows the path of normal stress unloading,and the damage of part of the rock mass shows obvious time-dependent characteristics.In view of this,this paper uses similar materials and homemade molds to prepare through-jointed rock specimens with different roughness,and conducts conventional straight shear tests with constant normal stress increasing shear stress,unloading straight shear tests with constant shear stress unloading normal stress,and shear creep tests with constant shear stress normal unloading in order to analyze the deformation and damage characteristics of the jointed rock mass under different conditions.The main research of this paper is as follows:(1)In this paper,conventional direct shear tests and unloading direct shear tests were carried out on five through-jointed rock masses with different joint roughness(JRC=0,5,10,15 and 20)using the HYZW-500 L direct shear rheometer.Through the experimental data,we analyze the influence law of nodal roughness on the strength and deformation characteristics and shear breakage characteristics of through nodal rock masses under different stress paths,and derive the shear strength formula and shear breakage mode for different nodal roughness,and then,based on the experimental analysis results,conduct a comparative study again(2)In this paper,the normal unloading shear rheology test is studied on different penetration joints of rock masses,the effect of graded unloading under different joint roughness on the shear rheological characteristics of through joint rock masses and the characteristic laws of deformation and damage under different unloading rheological conditions are analyzed,and the theoretical values of shear damage normal stress under unloading shear rheological tests are calculated by using the empirical formula for shear strength in unloading direct shear tests and compared with the actual values of unloading damage normal stress in actual unloading shear rheology.(3)On the basis of the normal graded unloading creep test,the unloading shear creep principal structure model study was carried out.By comparing the transient strain,creep strain and damage mode,it is found that the unloading shear creep properties of the through joints show good viscoelastic properties,and the Burgers intrinsic model is established by using the variation law of the test data,and the model parameters are fitted and verified by using the lstopt software;In addition,the creep rate of the unloading shear rheological test curve is analyzed,the rheological index n is introduced,and then an improved Burgers model is proposed,which is validated by fitting with lstopt software and the regular variation of the element model for different nodal roughness JRC.