Dynamic centrifuge tests on effects of isolation layer and cross-section dimensions on shield tunnels

An isolation layer, consisting of a rubber layer wrapped around the outside of a tunnel lining, acts as a countermeasure to enhance the safety of a tunnel during an earthquake. The main objective of the present paper is to verify the seismic efficiency of isolation layers in shield tunnels, and to study the influence of cross-section dimensions on seismic isolation effectiveness. Two sizes of shield tunnel model (with and without isolation layers) are prepared, and six groups of dynamic centrifuge tests are conducted. The test results show that the isolation layer effectively decreases dynamic bending moments in both large and small cross-section tunnels. The smaller cross-section tunnel with smaller ratio of tunnel diameter to isolation layer thickness has a greater reduction of structural response, because more soil deformation is absorbed.