Mechanical Analyses and Controlling Measures for Large Deformations of Inclined and Laminar Stratum During Tunnelling

The reasons why large deformations of inclined and laminar stratum occur in complicated geological conditions during tunnelling remain unclear. In this study, the geological conditions, the initial design of excavation and support and specific deformation failure modes of the laminar stratum and initial support system were first introduced at the Yangjiaping tunnel in China. Thereafter, field surveys, laboratory tests and numerical simulation were performed to investigate this complicated deformation and mechanical behaviour. Meanwhile, by combining buckling and catastrophe theory, the occurrence criteria of the deformation and failure of such stratum were established. Finally, excavation and support adjustments were proposed to control the rock mass deformation. The theoretical criterion reveals that buckling failure of the laminar structure has an obvious influence on the large deformation occurrence. By adopting the adjusted excavation and support measures, the rock mass deformation and contact pressure between the surrounding rock mass and initial lining are both dramatically decreased. The largest decline in the average horizontal convergence is approximately 25 cm; the maximum contact pressure value is approximately 1.149 MPa at the right haunch, which is about 64% of the value at the same location when using the original excavation and support method.