Single Arch Four-lane Highway Tunnel Failure Mechanism Model Test And Numerical Simulation

With the high steady increase of our national economy, large cross-section highway tunnel was adopted to meet the expanding requirement of the traffic quantity through mountain region. The form of arched structure with big span-ratio was used in the process of designing, but construction mechanics was unclear, some parameters just like lining thickness were depended on the experience values, and that can bring distortions and fractures in different degree to the tunnel lining structure after operation. Currently, the design code for the large cross-section highway tunnels was not carried out in detail. As a result of this, research on how to choose the lining parameters to guarantee the reasonable lining stress and tunnel safety deserves to be further studied.The research status at home and abroad on the large cross-section highway tunnels was discussed, based on the Longtoushan highway tunnel engineering, taking geometric similarity ratio CL=50 and bulk density similarity ratio Cr=1 as basic similarity ratio and grouping according to the surrounding rock grade, so as to control the complete similarity of various physical and mechanical parameters on the basis of similarity theory. Failure load of the tunnel lining under different surrounding rock grade was simulated by the loading of the jack, the contact pressure between the surrounding rock to the tunnel model and the lining, lining and the rockbolt were monitored in the experiment. Eventually the data collected by the earth pressure cells, lining strain, axial strain of rockbolts and radial displacement change value of the tunnel lining were obtained by the loading experiment of the laboratory model.Meanwhile, three-dimensional model was created by the finite difference software, lining stress law signatures, radial displacement change characteristics, bolt-shotcrete support mechanical laws and surrounding rock mass plastic zone change rules were analyzed under different surrounding rock grade and different conditions of unbias tunnel and bias tunnel when the tunnel lining structure endured by the upper loading. Finally, the data of the loading experiment of the laboratory model and the numerical simulation have been analyzed and compared, the characteristics of lining moment, axial force and the occurrence and development of fractures were obtained when the tunnel lining structure endured by the upper loading.