Seismic behaviour of shallow cut-and-cover tunnels

Abstract

With increased demand for urban space, there is a growing propensity to move urban lifeline systems like Metro systems, power, and water cables etc. to shallow, cut-and-cover tunnels. The seismic behaviour of such rectangular tunnels is important as these systems need to remain operational in the period after the earthquake for emergency rescue & recovery operations. Due to the large longitudinal extent of the tunnels, they pass through varying geological formations that can vary from loose, saturated sands to soft clay layers. In this paper, the main focus will be on determining the seismic response of shallow, rectangular tunnels that are passing through liquefiable, loose sand layers and very soft clay layers. The results from two separate centrifuge testing campaigns will be presented. The dynamic response of the tunnel will be compared to the input motion. The tunnel movement during seismic loading were obtained using high-resolution, high-speed imaging in combination with GeoPIV-RG software, as well as the linear variable differential transformers (LVDT). The uplift of the tunnel structure during the earthquake loading due to its high buoyancy relative to the soil body will be discussed. Finally, conclusions will be drawn on the effect of the soil strata through which the tunnel passes, based on the centrifuge data from loose, saturated sand, and soft clay tests.