Analytical solutions of two-liner tunnels constructed in time-dependent plastic rocks considering loading-unloading stress paths

Abstract

The mechanical behaviours of soft rocks are time-dependent and significantly influenced by the loading and unloading histories. The main objective of this study is to investigate the tunnelling behaviours of supported tunnels constructed in time-dependent plastic geotechnical materials, taking into account the tunnelling advancement, the viscoelastic-plastic behaviour of host rocks, sequentially installation of primary and secondary support systems, as well as the actual stress path throughout the entire excavation and construction stages. In the determination, the Burgers viscoelastic model and the unified strength theory respectively represent the time-dependency and plasticity of geotechnical materials. Furthermore, the interactions at both rock-support and support-support interfaces are considered. Finally, the time-dependent solutions of stresses, displacements, and supporting pressure are obtained, by using the compatibility and boundary conditions. As verification and validation steps, the results obtained from these solutions match well with numerical predictions and monitoring data. Finally, in the parametric analyses, the developed analytical solutions are performed to investigate the influence of the supporting time, and different material properties of host rocks and support systems on the stability of tunnels.