Methods for evaluating the seismic isolation performance of foam concrete shock-absorbing layers in mountain tunnels in high-seismic-intensity areas

Abstract Currently, a large number of post-earthquake surveys and statistical analyses of tunnel damage indicate that tunnels built against mountainsides are subject to the coupled effects of “asymmetric loads and seismic cyclic action,” which increase the risk of earthquake-induced damage to these tunnels. Therefore, the primary objective of this paper is to propose a new seismic mitigation method for mountain-adjacent tunnels to reduce structural damage to their linings under seismic loads. This method involves developing a mix design for a foam concrete shock-absorbing layer model material. Using a shake table test chamber, vibration tests were conducted on tunnel models representing shallow-buried, off-center-loaded mountain-side tunnels crossing existing potential slip surfaces, comparing conditions with and without the foam concrete shock-absorbing layer. The test results showed that without a shock-absorbing layer, slope failure is severe and localized, leading to a sudden increase in bending moments in the tunnel lining; whereas after installing the foam concrete shock-absorbing layer, the isolation layer significantly attenuates the seismic response of the tunnel lining, and the bending moments in the lining are markedly reduced. For the lining structure with the foam concrete damping layer, the bending moment values in the upper and lower compression zones, as well as the left and right tension zones, decreased by 13.6%, 8.6%, 11.3%, and 8.1%, respectively, compared to the corresponding measurement points without the damping layer. This indicates that the foam concrete shock-absorbing layer can reduce bending moments in the tunnel lining, mitigate seismic damage, and provide effective seismic resistance. Tests have shown that a foam concrete shock-absorbing layer can address the issue of insufficient seismic resistance in tunnels located near mountains in high-seismic-intensity zones.