Polyhedral Simulation Of Discrete Fracture Network In Rock Mass Of Hydraulic Engineering And Its Application

Rock masses,consisting of rock blocks and discontinuities,are non-uniform and anisotropic.The discontinuities play an important role in controlling mechanical properties,hydraulic characteristics and engineering stability of rock masses.However,probabilistic discontinuities represented by fractures are numerous,randomly distributed in terms of their geometric and statistical characteristics and usually cannot be directly observed,which makes it a key problem in studying rock mass structures.Discrete fracture network(DFN)proves to be an effective approach to solve this problem,and it has been extensively studied by researchers.Depending on water conservancy and hydropower projects,this paper propose a polyhedral simulation method for discrete fracture network in rock mass.It has been applied to calculation of 3D mechanical connectivity rate,block identification and stability analysis.(1)Based on Monte Carlo simulation method,2D Poisson process and 3D geological modelling technique,a novel simulation approach of generating polyhedrons for discrete fracture network was presented.This paper focuses on the simulation methods of fractures in terms of their shapes,sizes,apertures and fillers.In order to ensure the validity of the new fracture network model,numerical test and graphic inspection for simulation results are conducted.(2)A refined rock structure model is constructed by coupling geological body,deterministic structural planes,PDNF model and free surfaces.Based upon topology,precise modeling and identification analysis of complex block and block group are carried out.And the major characteristics and the refined modeling method of complex rock blocks and block-groups are analyzed.Finally,a modified and precise topology-based identification method of rock blocks and block-groups is put forward.(3)Based on the polyhedral discrete fracture network(PDFN)model,an enhanced projective approach for calculating 3D mechanical connectivity rate is proposed.In this method,the transfixion fractures are considered.By searching the 3D mechanical connectivity rates at different elevations in different dip directions and dips,the comprehensive shear strength parameters of rock mass can be estimated.Based upon surface block theory and refined 3D integrated rock slope model,the factor of safety(FOS)of single key block is calculated by the limit equilibrium method.The FOS of a block-group is computed by the Sarma method.Finally,the stability of rock slope is evaluated by comprehensive analysis.(4)A new stability analysis method for stochastic rock blocks is presented.The volumes of stochastic rock blocks are counted and the instability probabilities of stochastic rock blocks under self-weight and seismic condition are computed and added up.Then rock mass structure model is partitioned,and the maximum depth of the block,the block density and the block support intensity are analyzed.This provides an important reference for determining the support scheme of the tunnel blocks.