Study on Optimization of Composite Lining of Double-Track Haul Railway Tunnel

The research on the stress of composite lining is the basis of the design of composite lining. In practical engineering, the design scheme of composite lining is usually dominated by experience. In order to put forward a better design scheme of composite lining for railway double-track tunnel, based on field monitoring and numerical simulation, the lining optimization research is carried out by changing the thickness of spray mixing layer, the type of grid steel frame and the thickness of secondary lining. The optimal design scheme is determined by analyzing the influence of changing the above design parameters on the internal force of lining. The research shows that: 1) the optimal design scheme of the tunnel is 25 cm thick spray mixing layer, 40 cm thick grid steel frame H180, and 35 cm thick secondary lining arch waist and side wall; 2) The axial force distribution of the grid steel frame is characterized by' large arch, secondary side wall and small inverted arch’; 3) After changing the type of grid steel frame and increasing the thickness of mixing layer, the axial force borne by the grid steel frame decreases by 10%; 4) When the lateral pressure coefficient is 0.8, the internal force distribution of vault, arch waist and side wall is uniform, and the bending moment is at a low level; 5) Thinned secondary lining thickness increases the bending safety factor of the lining, and verifies the feasibility of the optimization scheme of thinned secondary lining 5~15 cm.