Simulation Of Rock Burst Of Surrounding Rock In Deep Tunnel Based On Discrete Element Method

It is an inevitable requirement of modern and future social development to construct a large number of deep underground tunnels,at the same time,Under the condition of deep burial,the change of the nature of surrounding rock may lead to rock burst disaster,which may lead to equipment damage,casualties and construction delay,and bring serious losses to the actual project.With the continuous advancement of China’s infrastructure construction and the deepening of underground space,the prevention and control of rock burst in China will become more and more prominent in the visible future,and become an important topic in the field of prevention and control of engineering geological disasters in deep underground space.Research on rock burst mechanism is an important basis for preventing and controlling rock burst disaster.Analyzing the physical process of rock burst,exploring the meso-mechanism of rock burst,looking for the key factors inducing rock burst and the engineering parts prone to rock burst disaster,in order to provide a certain reference for practical engineering and reduce or avoid the loss caused by rock burst disaster,which has important theoretical significance and practical value for the construction of underground space engineering.This paper takes 1^#diversion tunnel of Jinpingshan II Hydropower Station as the research object,the mechanical properties of the Baishan Formation marbles(T_2b)and the rock burst mechanism of the diversion tunnel are studied by the methods of controlled experiment,numerical simulation and theoretical analysis.I mainly analyzed the mechanical properties of rock,the influence of minimum confining pressure on rock burst,the influence of different lateral pressure coefficient and different excavation shape on rock burst.The main research contents of this paper are as follows:（1）Introducing the discrete element method and PFC particle flow program,and the principles,characteristics and applicability of the three bonding models in the discrete element software PFC were introduced.The simulation results of the two contact models were compared,and the flat joint model（FJ model）,which was more able to accurately reproduce the failure mode of rock under high stress,was selected for this simulation study.（2）Parametric analysis was carried out,and the corresponding relationship between individual microscopic parameters and peak stress,residual strength and elastic modulus as well as the interaction effect between each parameter were determined by using the complete test design method and the factorial test design method respectively,and the influence of relevant microscopic parameters on macro mechanical properties was qualitatively summarized.The number of cracks,the failure mode and the stress-strain curve were compared and analyzed with the control experiment,and a set of meso-parameters which could reflect the mechanical properties of the rock in the engineering area were obtained.Based on the simulation test results of marble in Jinping Baishan Formation,the tendency of rock burst is predicted and analyzed.（3）Indoor unloading rock burst simulation tests were carried out,the different confining pressures and load levels were set,monitoring the whole process of cracks,force chains,displacement and velocity of each group of samples,studying the influence of minimum confining pressures on rock burst and to explore the whole process of indoor rock burst phenomenon at the meso level.（4）The micro-mechanical parameters obtained from parameter inversion were reduced and applied to the two-dimensional tunnel excavation simulation test.Three kinds of lateral pressure coefficients and two kinds of tunnels with different excavation sections were set,monitoring the crack,force chain and displacement of the tunnel under each working condition,and then the stress criterion was used to predict the rock burst of the tunnel.The influence of subsection excavation on rock burst phenomenon of tunnel surrounding rock is studied by adding the simulation test of three-dimensional semi-circular tunnel excavation,and the mechanism of rock burst failure of tunnel is discussed comprehensively.