Abstract： Optimum design of composite lining structure is one of the important research topics in tunnel engineering. Too thick lining and too dense reinforcement not only cause economic waste but also may cause lining to crack easily. This research relies on the Zhengzhuang Tunnel of Menghua Railway, to study the lining thickness thinning through insitu test and theoretical analysis method. Firstly, according to the concept of ultimate bearing capacity curve of lining section, a method of evaluating lining safety by bending safety factor is proposed. Secondly, based on the monitoring internal force of lining section obtained from in-situ test, the variation characteristics of section internal force before and after lining thinning are obtained. After lining thickness thinning, the bending safety factor of lining section increases and the bending safety is improved. Finally, the in-situ monitoring results are verified through finite element calculation, that is the optimum design of composite lining structure with initial support strengthening and lining thickness thinning is feasible. The research results show that in the design of tunnel lining, if lining thickness is too large, the bending safety factor will decrease and lining is prone to crack due to too large section stiffness. So optimizing lining thickness properly is good for ensuring its bending safety. The research results have certain reference significance for the design of composite lining structure.
