A theoretical solution to investigate long-term behavior of pressurized tunnels in severe squeezing conditions

In this paper, an analytical-numerical method is presented to study the long-term behavior of pressurized tunnels. In this regard, the pressurized tunnel construction is simplified into three stages: tunnel excavation, installation of the lining, and applying the internal water pressure. The rock mass around the tunnel is assumed to obey the viscoelastic Burgers model and to have a permeability that is variable over time in any location. The tunnel lining is elastic and has constant permeability. To derive the equations, the coupled hydro-mechanical interactions are simulated and solved simultaneously to find out the tunnel displacements and lining pressures. After verifying the proposed method, a parametric study is conducted, and the influences of various parameters such as rock mass rheological parameters, the ratio of rock mass permeability to lining permeability, variation of rock mass permeability over time and distance, and magnitude of the internal water pressure are investigated. The obtained results show the significance of considering variable permeability on the tunnel performance. As well, the Maxwell shear modulus is the most influencing parameter among Burgers model parameters.