Block Stability Analysis Considering Structural Surface Cohesion Damage And Rock Bridge Damage Timeliness

Based on the field measurement data of a candidate site for underground disposal of nuclear waste,the following three aspects of research work are carried out on the basis of block identification.1.Discussion of the influence of tunnel excavation on the damage of cemented structural planes with different angles.2.Stability analysis of goaf block produced by tunnel excavation.3.Time-effect analysis of damage of rock bridge.The research contents and conclusions are as follows:(1)Study on cohesive force damage of cemented rock interfaces.Based on cohesive element and Quads Damage criterion,the damage of structural planes with different angles to tunnel azimuth is simulated by using finite element software program.The calculation results show that the maximum damage extent is between 40~0and 50~0for the tunnel wall.For displacement,attention should be paid to the inclination interval of two structural planes,45~0to 55~0,and 75~0to 85~0,among which the maximum displacement occurs between 75~0and 85~0.For the tunnel vault,its displacement tends to increase with the increasing of structural planes inclination,and the maximum and minimum displacements occur at 0~0and 90~0of structural planes inclination.(2)Block stability analysis.By applying explicit dynamic finite element method,the continuous-discontinuous deformation of fractured rock mass and local instability process of block composed of glued structural planes are simulated.Considering the initial in-situ stress,secondary stress induced by excavation,cohesive and tensile strength of structural plane,and friction stress between them,the stability of block is studied.The results show that the cohesive element can well simulate the damage characteristics of the cemented structural plane and the sliding behavior of the unstable blocks.It can be used as a calculating tool for the stability analysis of blocks.The progressive damage process of the structural plane also provides a new idea for simulating the time-dependent expansion of rock bridge.(3)Time-effect analysis of damage model of rock bridge.Through the Vusdfld subroutine interface of explicit dynamic finite element module,the stress of material integral points is obtained by using the Vgetvrm function provided,and the time-dependent subcritical crack growth of three-dimensional rock bridge is studied by considering three modes of crack propagation(mode I-tension,mode II-in-plane shear and mode III—out-of-plane shear).In the subroutine,the length of rock bridge is represented by the state variable State New(k,1),Chge is the rate at which the rock bridge decreases step by step with time.So we can get the length of rock bridge varying with time dt.We can combine the failure of rock bridge with time,and then we can analyze the time-effect of rock mass failure.