Direct shear test on the interface between tunnel linings

Abstract The lining interfaces of composite linings typically include two interfaces: the primary lining–secondary lining interface and the primary lining–waterproof layer–secondary lining interface. These interfaces are observed in Chinese highway tunnels with weak surrounding rock. In order to ascertain more effective measures to accommodate the deformations between tunnel linings, it is necessary to investigate the shear resistance performance of the interfaces and the factors that influence this performance. The samples are classified according to the presence or absence of waterproof layers, cohesive interfaces, and rough interfaces. Subsequently, direct shear tests are conducted under constant normal stress. The shear rate is 1 mm/min, and the normal stress is 0.5, 1.0, and 2.0 MPa, respectively. The results of the tests demonstrate that the shear properties are influenced by the normal stress, the waterproof layer, the cohesive interface and the rough interface. The shear resistance performance of the lining interface in the absence of a waterproof layer is observed to be superior to that observed with a waterproof layer. The normal compressive stiffness range for the primary lining‐secondary lining interface is observed to be between 0.69 and 3.17 GPa, with a pre‐peak shear stiffness range of 0.12–1.88 GPa. The effective cohesion range is found to be between 0 and 0.29 MPa, while the internal friction angle range is observed to be between 22.62° and 29.43°. In contrast, the normal compressive stiffness for the primary lining–waterproof layer–secondary lining interface is observed to be within the range of 1.24–9.78 GPa, the pre‐peak shear stiffness range is 0.45–39.68 GPa, the effective cohesion range is 0.07–1.98 MPa, and the internal friction angle range is 34.92°–52.24°. In conclusion, this investigation presents a number of potential measures that could be employed to enhance the shear resistance performance of tunnel lining interfaces. Furthermore, it furnishes a set of parameters derived from the test results that could serve as a foundation for subsequent research and design endeavors.