Numerical modelling of centrifuge tests on tunnel-soil systems

The number of tunnels in seismic regions has grown significantly in recent decades. It has usually been assumed that tunnels perform better than surface structures during seismic events. However, recent cases have shown that tunnels can be significantly damaged by seismic events. Thus, an evaluation of their response to earthquakes has become increasingly necessary. This paper presents a FEM blind prediction of centrifuge tests on a reduced scale tunnel. The main objective of the paper is to evaluate the numerical model that reproduces the response recorded in the centrifuge. The centrifuge tests involved a tunnel in dry sand. The numerical simulation was performed on the physical-scale model of the transverse direction of the tunnel, which is of prime importance, as it can show large stress-strain levels in the tunnel lining. The tunnel behaviour was assumed to be visco-linear-elastic, while the soil behaviour was assumed to be visco-elastic-perfectly plastic. The soil model parameters were calibrated on the basis of laboratory tests performed on the sand used for the test. The comparison between the experimental and numerical results is presented in terms of acceleration in the time and frequency domains. The experimental and numerical settlements of the sand surface and displacements of the sand-tunnel system, as well as the bending moments and hoop forces acting in the tunnel are also compared. Increments of the bending moments and hoop forces are also evaluated using the closed-form solution proposed by Wang (Seismic design of tunnels: a simple state-of-the-art design approach. Parson Brinckerhoff, New York, 1993) and Penzien (Earthq Eng Struct Dyn 29:683-691, 2000). A very good agreement between the experimental and numerical results is achieved in terms of horizontal acceleration time-histories and their Fourier spectra, as well as in terms of vertical displacements of the sand surface. Moderate differences exist between the experimental and numerical bending moments and hoop forces; experimental, numerical and analytical increments of the bending moments and hoop forces are in a quite good agreement with each other.