Bearing capacity of composite tunnel lining in soft rocks: Large-scale model test

Composite lining is widely used in tunnel engineering due to its high strength and adaptability. For current model tests on tunnels with composite lining, a large geometric similarity scale resulted in a small-scale model. Failure process and force of supports are difficult to observe and measure. Research exploring the bearing capacity of tunnels with composite lining is also limited. To overcome the above deficiencies, a model test method to investigate the bearing capacity of tunnels with composite lining in soft rock is proposed. A large-scale model test system with a similarity scale of 12.5 is developed. Similar materials of surrounding rock, rock bolt, first and secondary lining are determined by triaxial test, tensile test, and pull-out test. The monitoring scheme is designed to obtain the stress of the surrounding rock, rock bolt, first and secondary lining. Model tests for tunnels without lining, with composite lining and with dense composite lining are conducted. Complete loading processes are observed, and the bearing capacities are explored. Displacements and stresses of surrounding rock material are discussed. Evolution variations of axial force of rock bolt, stress distribution of first and secondary lining for tunnel with composite lining and tunnel with dense composite lining are compared. The effect of rock bolt densification is investigated. The results indicate that total loads transferring to both first and secondary lining at any area of tunnel are roughly equivalent. There is a ‘mutual balance’ effect between axial forces of them. Densification of rock bolt results in greater axial forces of first lining and rock bolt but smaller axial force of secondary lining. • Similar materials for surrounding rock and supports are elaborately determined. • Large-scale model test system with a similarity scale of 12.5 is developed. • Failure processes and bearing capacities of three test conditions are explored. • Evolution laws of different supports for two test conditions are compared. • Effect of densification of rock bolt on various supports is investigated.