Seismic response of deep circular tunnels subjected to S-waves: Axial bending

Ovaling deformation of circular tunnels has received great interest from the tunneling community because this mode of seismic-induced deformation is considered the most critical. However, there is growing evidence that other deformation modes can also be important and thus need to be considered in design. This study presents a new analytical solution to estimate axial bending (snaking), a mode of deformation caused by S-waves impinging on a tunnel parallel to the tunnel axis. The solution is developed using the soil-structure interaction approach with the assumption that the interface between the ground and the tunnel lining is frictionless (full-slip). Full dynamic numerical simulations are conducted to verify the new full-slip solution, together with the existing no-slip solution. Effects of dynamic amplification are also explored for both full-slip and no-slip interface conditions by changing the wavelength (or frequency) of the seismic input motions.