DEM Simulation Analysis Of Size Effect Of Jointed Rock Mass And Its Multi-Scale Calculation Method

As the construction scale and complexity of our country's tunnels and underground projects continue to increase,related engineering problems that may be encountered in engineering construction are also gradually increasing.As an important carrier in engineering,rock mass contains many joint defects of different scales ranging from meso,macro to engineering scale.It has strong non-uniformity and size effect,which makes the engineering rock mass under external load,the mechanical response of rock mass is the result of the coupling of mechanical behaviors at different scales.Therefore,its mechanical properties have obvious multi-scale characteristics and complexity,which brings many challenges to engineering construction.Research on the corresponding size effects of engineering-scale rock masses and obtaining the representative unit volume(REV)of the rock masses have become the basis for multi-scale engineering rock mass stability analysis and catastrophe mechanism research.Therefore,it is urgent to propose a multi-scale analysis method of engineering rock mass which can consider both the micro-structural mechanical behavior,the macroscopic deformation and failure characteristics of engineering rock mass,so as to break through the limitation of the inherent adjacent scale calculation and analysis method.Based on the Yao jia yu Tunnel Project in the Bin-Lai Expressway Reconstruction and Expansion Project,this paper conducts a systematic study on the size effect of the engineering jointed rock mass and the influencing factors of the representative unit volume(REV),and finally uses the obtained jointed rock mass representative unit to propose a multi-scale calculation method based on the jointed rock mass characterization unit body and applied it to the supporting engineering.The specific research results and conclusions are as follows:(1)Using tunnel 3D laser scanning technology,combined with on-site high-definition digital camera and manual window measurement method,the tunnel face structural surface information is collected and counted,and the statistical feature values corresponding to the joint geometric parameters of the tunnel face are obtained.The distribution probability and eigenvalues of discrete structural surface network simulation parameters such as structural surface occurrence,structural surface nature and size,location,density,etc.,are established,and a three-dimensional discrete structural surface network model that can reflect the true distribution of tunnel face is established.(2)Through the synthetic rock mass technology,a multi-scale synthetic rock mass model reflecting the real spatial distribution of structural planes was constructed,and the uniaxial compression simulation test of the synthetic rock mass and the triaxial compression simulation experiment under different confining pressure conditions were carried out to reveal the size effect of the jointed rock mass is obtained,and the representative unit volumes(REV)of the uniaxial compressive strength,triaxial compressive strength and elastic modulus of the surrounding rock are obtained,the size are both 6m×6m×12m.The jointed rock under the condition of triaxial compression under different confining pressures,the change law of the REV is:as the confining pressure increases,the size of the mechanical parameter REV of the jointed rock mass has a decreasing trend.(3)The uniaxial compression numerical simulation test of synthetic rock mass models of different scales were carried out,and the influence of geometric parameters such as joint trace length,spacing,and inclination angle on the uniaxial compressive strength and elastic modulus of jointed rock masses was investigated.Within a certain range,as the trace length increases,the uniaxial compressive strength REV size decreases,and the elastic modulus REV size shows a trend of first decreasing and then stabilizing;with the increase of joint spacing,the uniaxial compressive strength and elastic modulus REV size of rock mass also increase.With the increase of joint inclination angle,the REV size of uniaxial compressive strength of rock mass becomes smaller.The REV size of the elastic modulus decreases first and then approaches to stability.(4)Based on the open-source discrete element program YADE and the open-source finite element program OOFEM,a rock-mass characterization unit body is used as the connection,and a finite element-discrete element coupling multi-scale analysis method based on the rock mass characterization unit body is proposed,which improves the multi-scale analysis.The feasibility and accuracy of the multi-scale coupling calculation method are verified by the comparison test of rock biaxial compression numerical simulation.The method has been successfully applied to the Yao jia yu tunnel project of Bin-Lai Expressway,which solves the problem the engineering scale calculation problem of the project.