A case study of the failure of Liziping tunnel

Liziping Tunnel is located in the southwestern mountainous area of China. The majority of the support structures in the tunnel have failed shortly after construction completion. The goals of this study are to reveal the failure cause of the given support structure, and to develop a quantitative analysis method to optimize scheme of support design. According to the parallel model, the deformation-load relation function of combined support structure (CSS) of anchor bolt-spray are derived from the bearing arch mechanism. Through numerical simulations, the ground reaction curve (GRC) of country rock is obtained, along with the longitudinal deformation profile (LDP) reflecting influences of both installed supports structure and construction technology. The stability factors of the installed support structure under various envisaged construction schemes are estimated by using the convergence-confinement method (CCM). The results indicate that it is possible to avoid the failure of the given support structure if the construction technology is slightly adjusted during construction. Derived from the above research, the empirical method based on the rock mass classification is expanded to be a quantitative analysis approach and can consider more contributing factors than ever, through embedding the convergence-confinement algorithm into the empirical design method of support scheme and with the help of simulation computation technology.