Abstract: Herein, a largescale tunnel structural model experimental system is established. First, loaded damage tests are conducted on tunnels without support, supported by shotcrete of various thicknesses, and supported by secondary lining through structural tests to validate the feasibility of the load structure model of the shotcrete layer using the total safety factor method and its calculation method. The physicomechanical parameters of each material in the model test are then clarified through triaxial tests of the surrounding rocks and fine sand materials. The entire loaded damage process of the tunnels without support, supported by shotcrete of various thicknesses, and supported by secondary lining, is simulated. The designed bearing capacity of the shotcrete and secondary linings is determined according to tunnel failure states. The stress and strain of the surrounding rocks, internal and external strain of the shotcrete layers, and displacement of the shotcrete layers are monitored. Finally, the deformation and stress characteristics of shotcrete and secondary linings are analyzed for determining the bearing capacity of these materials. Comparing the results with the calculated results using the total safety factor method shows the following: (1) The stress of the shotcrete layer exhibits a small eccentric compressive stress. The cohesion between the shotcrete lining and surrounding rock mass can transfer the shearing force in the rock mass, reducing the bending moment and greatly improving the compressive strength of the shotcrete lining. The designed bearing capacity of the shotcrete lining is higher than that of the secondary lining under the same thickness. (2) The designed bearing capacities of the shotcrete lining with thicknesses of 2 and 4 cm are 27.0% and 22.9% higher, respectively, than the theoretical calculation results by the total safety factor method, indicating the rationality of the calculation model of the bearing capacity of the shotcrete lining by the total safety factor method.

Key words: tunnel, support structure design, shotcrete layer; model test, total safety factor method, destructive test, bearing capacity