Equivalent Discontinuous Modeling Method Of Jointed Rock Masses For DEM Simulation Of Mining-induced Rock Movements

The Discrete Element Method(DEM)is of obvious and inherent advantages in simulating large displacements and discontinuous deformations of rock masses,and suitable to simulate the mining-induced rock movements.However,when the DEM calculation model size is large,the rock mass in the model range often contains a large number of actual joints.If the calculation model is built according to the distribution of these actual joints,the calculation model of DEM will consist of a large number of blocks,which would lead to the impossibility of numerical calculations due to the insufficient computer memory.To address this problem,an Equivalent Discontinuous Modeling Method(EDMM)of jointed rock masses for DEM simulation of mining-induced rock movements is proposed in this paper.In this method,an actual geological body with a complex joint system will be simplified into an Equivalent Discontinuous Model(EDM),which is a DEM calculation model with a simplified hypothetical joint system.Since the hypothetical joint systems in EDM were simplified from the actual joint system,their joint mechanical parameters are differing from that of actual joint system.Thus,it is essentials to determine the joint mechanical parameters of the simplified hypothetical joint system in EDM.The approach for determining the mechanical parameters,i.e.,the cohesive strength(C),the internal friction angle(?),the joint normal stiffness(JKN),and the joint shear stiffness(JKS),of the hypothetical joints of the EDM is the core of the proposed EDMM.The main procedure of the proposed EDMM is composed of:(1)determining REV values for the selected joint spacing(5m,10 m,20m,30 m and 40m);(2)building a group of Equivalent Discontinuous Cube Models(EDCMs)for each subarea of an EDM,with different joint spacing based on the identified REV sizes;(3)determining the joint mechanical parameters of each EDCM based on the mechanical properties of the actual rock masses of the subarea;(4)establishing the relationships between the joint spacing and joint mechanical parameters for each subarea of EDM;and(5)determining the mechanical parameters of the hypothetical joints in each subarea of the EDM based on the built relationships function between joint spacing and joint mechanical parameters.To demonstrate its applicability,the proposed EDMM was employed in two case study: 1)to simulate the pattern of rock mass movements and failure condition that triggered by underground mining at the western open-pit final slope of Yanqianshan iron mine;and 2)to evaluate the stability condition of open pit slope and calculate the FOS of the Southern open pit slope of Yanqianshan iron mine.To validate the reliability of the proposed EDMM the pattern of rock mass movement and failure condition that simulated by EDM were compared to the rock mass movement and failure condition that observed from the actual field work.The slope FOS calculated by EDM also compered to the slope FOS that determined through ECM approach.In both case studies the EDM simulation results have a good consistency with that of the actual field observation results which indicate the good applicability of the proposed EDMM to simulate the discontinuous rock mass movement that induced by mining activities.