Load laws of composite lining in mountain tunnel model tests and numerical simulation validation

Currently, model tests are increasingly being used to simulate the construction of mountain tunnels, but the support structure of the model tests does not show the composite lining, and the force laws of the composite lining are not yet clear. In this research, the force variation of composite lining under three cases in model tests of deep-buried tunnels were carried out with the surrounding rock grade and installation time as the variation factors. The test results reveal that: (1) The suitable method to reduce the contact load between the secondary lining and primary support is to enhance the primary support in the soft and weak surrounding rock. Correspondingly, for Class Ⅲ surrounding rock and better quality of surrounding rock, the primary support can lag behind the excavation face a certain distance. (2) The axial forces of the bolts tend to rise with concentration of 0.4 kN−0.7 kN after the secondary lining was installed. (3) With or without two to three excavation cycles delayed, the load sharing ratio of the secondary lining of the Class Ⅲ surrounding rock is less than 10%. Finally, the numerical simulation verifies the feasibility of the model tests.