Study On Stability Of Jointed Rock Tunnel Based On Discontinuous Deformation Analysis

In recent years,the scale and quantity of tunnel construction projects in China have continued to expand.At the same time,in the process of tunnel construction,the engineering geological conditions are becoming more complex and changeable.In response to such problems,there are still many imperfections in existing theoretical and technical means.In the construction of tunnel engineering,jointed rock mass is a common geological condition.Due to the existence of the discontinuous medium joint,the deformation of the rock mass medium shows the characteristics of discontinuous and large deformation,which brings many hidden dangers to the engineering safety.Therefore,in tunnel engineering,sufficient attention should be paid to the deformation prediction of rock masses with joints.In view of the engineering rock mass as a discontinuous medium,the discontinuous deformation analysis(DDA)theory provides a unique analysis method,which fully considers the complexity of the rock mass and has broad application prospects.Based on the previous research results,this paper carrys out the application research of discontinuous deformation analysis method.(1)The characterization methods of joint and fissure parameters are summarized,and the basic theory of DDA method and the original DDA program are systematically sorted out.This paper summarizes Barton's method for determining mechanical parameters of rock mass joints and details of its application.For the geometric parameters of rock mass joints,the track length and spacing of joints generally follow a negative exponential distribution,and the inclination and tendency of joints generally follow a normal or lognormal distribution.At the same time,the computer generated random variables which conform to the corresponding distribution function are elaborated.For the classic discontinuous deformation analysis method,the displacement parameters,displacement modes and mutual contact forms describing the deformation of the block are discussed,and the general equilibrium equation of the block system and the details of the derivation are explained.The shortcomings of the original DDA program are discussed and summarized,and the shortcomings of the original DDA program in the preprocessing part,the calculation and solving part,and the post-processing part are discussed in detail.(2)Based on the analysis of basic theory of discontinuous deformation analysis method and DDA source program,some key algorithms involved in program implementation of discontinuous deformation analysis method are analyzed and corresponding solutions are proposed.The program of discontinuous deformation analysis method involves a variety of key algorithms,including vector calculation,geometric analysis and matrix related algorithms.Vector method abstracts actual joint lines,blocks,etc.into data in computer.Vector calculation achieves the processing of entities through inter-vector operation.Geometric analysis involves the position relationship of joint line segments,"cutting" joint lines to find loops,geometric properties of polygon blocks,position relationship between points and blocks,etc.Matrix-related algorithms mainly include the trigonometric decomposition of matrices,the basic principle and implementation steps of over-relaxation iteration method,etc.(3)In view of the shortcomings of the original DDA program,the original DDA program was partially modified to make up for the deficiencies of the original DDA program in modeling,calculation and solution,and post-processing.For the shortcomings of the pre-processing of the original DDA program,this paper compiles the input file conversion table and program,and at the same time improved some problems in the randomness of joint parameters.In the modeling of tunnel excavation,the role of initial support is considered,and the material setting procedure is improved.In the calculation solution procedure,damping is added and a new general equilibrium equation is formed.In the post-processing,the post-processing program is improved to fetch more information about the calculation results and to add more content for display.(4)Based on the modified discontinuous deformation analysis method,the stability of actual tunnel engineering is analyzed and compared with the measured data.A numerical experiment is carried out to investigate the influence of joints on surrounding rocks during tunnel excavation.The parameters of the joint inclination and friction angle are changed to simulate the tunnel excavation.The deformation and stress of chamber and surrounding rock are analyzed when joint inclination and friction angle change,and the regularity in some cases is analyzed.The change of joint angle affects the deformation position of tunnel and the failure form of surrounding rock.The change of joint friction angle affects the displacement of block and its development trend.