Centrifuge modeling of seismic loading on tunnels in sand

The purpose of the work is to provide an experimental benchmark on the seismic behavior of tunnels, with the final aim of calibrating numerical and analytical design methods. A series of plane strain centrifuge tests with dynamic loading on a model tunnel was therefore carried out at the Schofield Centre of the Cambridge University Engineering Department (CUED). Four samples of dry uniform fine sand were prepared at two different densities, in which an aluminum alloy tube was installed at two different depths. The tube was instrumented with strain gauges in order to measure hoop forces and bending moments at significant locations. In order to monitor the amplification of ground motion from the base to the surface, vertical arrays of accelerometers were placed in the soil model and along the box. The instrumentation also included LVDTs that measured the soil surface settlement during all test phases. The test procedure and the results are described in the paper, showing the evolution of both accelerations and internal forces along the tunnel lining during the model earthquakes.