Analysis On The Long-Term Stress Of Tunnel Structure Under Soft Rock Creep Behaviors

With the tunnel engineering have gradually extended to the remote areas in Western China,soft rock geological conditions are often encountered.Soft rock has strong creep effect.The continuous deformation under in-situ stress leads to the increasing external loads on tunnel lining structure,which brings great challenges to the design of tunnel lining structure and seriously threatens the long-term safe operation of tunnel.Based on a soft rock diversion tunnel project,this paper studies the influence of soft rock creep behaviors on the long-term stress of tunnel lining structure under mudstone formation condition by means of theoretical analysis,data fitting numerical simulation and regression analysis.The main research work is as follows:Using rock mechanics test system,the uniaxial compression,triaxial compression and uniaxial creep compression tests of mudstone specimens were carried out.The complete stress-strain curves and graded creep curves of mudstone under different moisture and confining pressures states are obtained.?1?The classical rock creep model and its applicable conditions are analyzed.Based on the uniaxial compression creep test results of tunnel mudstone samples,Burgers model is selected to describe the creep characteristics of mudstone,and the model parameters are identified by 1stOpt software.By comparing the fitting creep curve with the creep test data,it can be judged that the Burgers model can well simulate the creep characteristics of mudstone samples.?2?Based on the principle of multiple linear regression analysis and numerical calculation method of FLAC^3D,a three-dimensional geological model of soft rock section in tunnel engineering area is established,and the initial stress simulation values of borehole location under six working conditions of gravity stress field and tectonic stress field are calculated.According to the measured results of initial stress field,the linear regression equation of initial stress field in soft rock section of tunnel is obtained.The value and distribution characteristics of initial stress field on the axis of soft rock section of tunnel are explored.?3?The numerical model of creep stratum-structure of soft rock is established by using finite difference software FLAC^3D.The Burgers creep model is used to analyze the influence of creep effect of soft rock on the long-term stress of tunnel structure.Based on this model,the influence of creep behaviors of surrounding rock on stress and deformation of tunnel structure under different initial stress fields is analyzed,and the long-term safety of general section lining and extended section lining of tunnel is studied.?4?The commonly used control countermeasures and principles for long-term stress of tunnel under creep behaviors of surrounding rock are studied.Based on the numerical model of soft rock creep stratum-structure,the effects of bolt-grouting support and flexible compressible layer on controlling creep effect of surrounding rock on the secondary lining structure of tunnel are proved respectively.