Study On Mechanical Characteristics And Supporting Stability Of Loess Tunnel

When building oil and gas pipeline tunnels in the loess layer,due to the engineering specificity of loess,such as collapsibility,vertical joints,loose porosity,etc.,serious damage may happen.If they are not handled properly,like improper support measures or inadequate support,they will lead to excessive deformation of the surrounding rock and damage to the support structure,which will seriously affect the construction progress.Based on much literature review,indoor testing and finite element numerical analysis,this Paper study and summarize the engineering characteristics of the surrounding rock of loess tunnels,the stability of loess tunnel slopes,and the support structure system of loess tunnels.The results of main research are as follows.1.The shear strength of loess under different moisture content and dry densities is obtained by using direct shear ap Paratus and triaxial ap Paratus,and the variation law of shear strength with water content and dry density is obtained.With the stress-strain averages from related experimentals,Parameters are brought into the ‘Duncan-Chang hyperbola model’,and the a,b in stress-strain Constitutive Relations under different confining pressure are obtained.This Paper uses E-v model of Duncan-Chang hyperbola model to program,and its result is applied in following simulation research.2.Based on limit equilibrium method and dynamic strength reduction method,this Paper uses finite element software to calculate the safety factor of loess tunnel slope.The effect of tunnel position on slope is also studied through numerical simulation.Indoor experiment simulation is tested for supporting effects of multiple pre-reinforcement methods near tunnel openings.The supporting effectiveness is evaluated through monitoring the displacement of land surface as well as the soild pressure.3.Study on the determination of surrounding rock load of loess tunnel.With the three-dimensional finite element software,the thnnel in Pingliang,Gansu province is simulated with different vertical joint distance(1m,2m,3m)and different vertical joint depth(5m,10 m,15m).Through com Parison and analysis of surrounding rock deformation,surface settlement,vertical joint misalignment,and initial support internal forces,the law of adverse effects of primary vertical joints on tunnel construction was obtained.4.Through the research and analysis on the supporting structure mechanism of the loess tunnel,combined with existing engineering experience,the reasonable supporting Parameters of the loess tunnel are proposed.