Interaction between strengthening and isolation layers for tunnels in rock subjected to SH waves

The strengthening and isolation are two types of strategies to reduce seismic damages to tunnels in rock. However, few closed-form analytical solutions for their seismic responses when tunnels are subjected to SH waves have been proposed. Therefore, based on the Xianglu Mountain Tunnel in Western China, which is located in a very active seismic territory, a close-form analytical solution was presented for the scattering problem of SH waves by the strengthening layer-isolation layer-lining system using the wave-function expansion method. A parametric study was then conducted to study the effects of the isolation and strengthening layers on the dynamic responses of tunnels in rock. The results show that the isolation layer can remarkably reduce the stress in the lining, but at the same time may lead to an increase in rigid displacement; the strengthening layer can stabilize the rigid displacement and further reduce the stress in the lining, but this effect is limited by the construction technologies used in actual projects. For tunnels in high-intensity regions, the isolation layer may collaborate with the strengthening layer. Owing to the existence of the strengthening layer, a relatively large modulus and a relatively small thickness can be chosen for the isolation layer. As a result, the collaboration between the isolation and strengthening layers can not only effectively reduce the stress in the lining but also stabilize the rigid displacement.