Dynamic strength of lined tunnel in hard rock medium under cylindrical unloading waves with visco-elastic interface effect

In deep rock medium excavation, the unloading waves due to the blasting excavation can bring great damage to the neighboring structures. In this paper, the visco-elastic interface model is introduced to study the dynamic strength around an existing lined tunnel subjected to blasting and unloading waves. Three unloading paths because of tunnel blasting excavation are considered, and the dynamic interface stresses of existing lined tunnel resulting from these unloading paths are derived. To describe the wave fields around the existing tunnel and in the tunnel lining, the wave function expansion method is used, and the elastic and viscosity coefficients of interface is used to describe the interfacial characters. The analytical solutions of displacement and stress fields in the rock mass are obtained. An approximate numerical integration method is introduced to calculate the displacements and stresses around the existing tunnel. In numerical examples, the circumferential stress around the existing tunnel under different interface parameters, unloading paths and geometrical and physical parameters of tunnels is analyzed. Comparison with the existing numerical results validates this model.