Application Of Discrete Fracture Network Simulation In Stability Evaluation Of Deep Chamber In Beishan Underground Research Laboratory

In June 2021,the construction of Beishan Underground Laboratory,the first underground research laboratory(URL)for geological disposal of high-level radioactive waste in our country,started construction,marking that China’s high-level radioactive waste disposal has officially entered the stage of underground research laboratory research and development.The host rock of Beishan underground research laboratory site is mainly granite.The joints and fractures in the rock mass are the weak surfaces of the mechanical properties of the rock mass,and their geometry and combination characteristics have an important influence on the stability of the surrounding rock of the underground chamber.This paper takes the host granite mass of Beishan underground research laboratory as the research object,analyzes the distribution law of rock mass fracture occurrence,trace length,density and other parameters,and obtains the data of each parameter of rock mass fracture.By using the discrete fracture network-discrete element coupling method,an equivalent rock mass reflecting the distribution state of the real rock mass in Beishan granite is constructed.Based on the physical and mechanical parameters of the rock mass and rock mass fractures in the Beishan underground laboratory site,the equivalent rock mass was assigned,and an iterative simulation operation was carried out,for the purpose to study the stability of the chamber to be built at a depth of 560 m underground..The main conclusions are as follows:(1)The method of numerical simulation of fractured surrounding rock using discrete fracture network-discrete element coupling provides a simple,fast and effective method for predicting and analyzing the stability of underground chambers in Beishan underground research laboratory.This method can provide reference and basis for the construction and operation safety of underground laboratory for geological disposal of high-level radioactive waste in the future.(2)The surface fractures distributed in the site area can be divided into 4 dominant groups of rock mass fractures,and the inclination and dip angle of each dominant group conform to the law of normal distribution function.The size of the fracture,namely the diameter of the fracture disc,is distributed according to the log-normal distribution function.The linear density of rock fracture conforms to the negative exponential distribution law,and the surface density and bulk density of rock fissures are calculated based on mathematical statistics and spatial geometric means.(3)Under the existing conditions,the discrete fracture network-discrete element coupling method is used to simulate and analyze the stability of the deep chamber in the underground research laboratory.But the amount of deformation is small.The excavation will lead to stress redistribution in the surrounding rock of the chamber,while the stress concentration occurs at the intersection of the fracture and the chamber excavation surface.At the staggered place between the chambers,unstable blocks may be formed,and protection of those places is required and extremely important during practical construction phase.