Numerical Simulation Of Rock Mass Mechanical Parameters And Size Effect Considering The Influence Of Microcracks And Joints

Rock mass,as a kind of natural geological material,usually forms joints,faults,fissures,micro-fissures,micro-pores and other defects in its interior due to crustal movement and other reasons.These defects can be divided into two categories according to geometric size: macro defects and micro defects.The existence of defects makes the rock mass show heterogeneity,discontinuity and anisotropy.The discrete element analysis software PFC based on particle flow can directly construct the equivalent model of fractured rock mass by generating a random fracture network(DFN).In this paper,numerical simulation tests are performed on the basis of many laboratory tests to study the mechanical properties and size effects of fractured rock mass with different density.The main contents and conclusions are as follows:(1)The orthogonal test scheme is designed and the related macroscopic parameters of rock quality are obtained by numerical test.The correlation between macroscopic and mesoscopic parameters was determined by multivariate analysis of variance,and the relationship formula between the two was determined by the stepwise regression analysis.Then the calibration process of mesoscopic parameters was determined and the accuracy was verified.(2)The mechanical parameters of rock mass with micro-defects were analyzed,and the rock mass models with different micro-crack densities were constructed and numerical tests were carried out.The crack initiation strength,type and number of secondary micro-cracks were analyzed by uniaxial compression tests.The cohesive force,internal friction Angle and peak strength under different confining pressures were analyzed by triaxial compression test.The variation of tensile strength with microcrack density was analyzed in the Brazilian splitting test,and the relationship between tensile strength and microcrack density was quantitatively expressed by the fitting formula.(3)For uniaxial compression test,the size effect of uniaxial compressive strength and elastic modulus and its REV size of micro-fractured rock mass are analyzed.For triaxial compression test,The changes of peak strength and elastic modulus under different confining pressures were analyzed,and the changes of REV sizes under the confining pressures of 5MPa and 10 MPa were also analyzed.(4)The study on the size effect of micro-flawed rock mass is extended to macroflawed rock mass,and the REV size determined by micro-fractured rock mass before is used as the initial model size of macro-jointed rock mass.The jointed rock mass is divided into two groups to study the influence of different structural characteristics of joints on the size effect.One group of rock mass has the same joint density but different dominant dip Angle,and the other group has the same dominant dip Angle to change the rock mass joint density.Uniaxial compression test was carried out to study the size effects of uniaxial compressive strength and elastic modulus of the two groups of rock mass,and the influence of the dominant joint dip Angle and joint density on the rock mass REV size was analyzed.