Correct evaluation of shear modulus and damping characteristics in soils under dynamic loading is key to both the fundamental understanding of soil behavior and the practical application of soil modeling programs. Dynamic centrifuge tests can contribute significant information about soil behavior, but great care must be taken over the signal processing techniques involved, and the test conditions are different from the laboratory experiments that form the database of existing knowledge. This paper outlines several factors that require careful consideration when deriving stiffness and damping parameters from centrifuge data. Shear modulus and damping degradation curves for a dry sand, saturated sand, soft clay and a model waste are then evaluated to explore some of the factors that are introduced during centrifuge tests. Stiffness is seen to be a more reliable parameter than damping ratio. Damping during centrifuge tests for certain materials appeared to differ from the expected values.

Tunnels in seismically active areas are vulnerable to adverse effects of earthquake loading. Recent seismic events have shown that there is a need to validate current design methods to better understand the deformation mechanisms associated with the dynamic behaviour of tunnels. The research described in this paper consists of physical and numerical modelling of circular tunnels with dynamic centrifuge experiments and complementary finite element simulations. The aim is to develop an understanding of the effects of tunnel depth on the seismic behaviour of tunnels. Tunnels with different depth-to-diameter ratios were tested in dry, loose silica sand. Accelerations around the tunnel and earth pressures on the lining were measured. A high-speed digital camera was used to record soil and lining deformations. Particle image velocimetry analyses were carried out on the recorded images to measure the deformations. Complementary dynamic finite element simulations were also conducted with a code capable of managing contact simulations at the soil–lining interface. Measurement of centrifuge experiments and finite element analyses show that the tunnel shifts from a static equilibrium to a dynamic equilibrium state as soon as the earthquake starts. The nature of the dynamic equilibrium, however, is difficult to predict using conventional analysis methods.

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 to measure hoop forces and bending moments at significant locations. 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 linear variable differential transformers (LVDTs) that measured the soil surface settlement during all test phases. The test procedure and the results are described in this paper, showing the evolution of both accelerations and internal forces along the tunnel lining during the model earthquakes.

A series of dynamic centrifuge tests were performed on a flexible aluminium square tunnel model embedded in Hostun dry sand. The tests were carried out at the centrifuge facility of the University of Cambridge in order to further improve knowledge regarding the seismic response of rectangular embedded structures and to calibrate currently available design methods. The soil–tunnel system response was recorded with an extensive instrumentation array, comprising miniature accelerometers, pressure cells and position sensors in addition to strain gauges, which recorded the tunnel lining internal forces. Tests were numerically analysed by means of full dynamic time history analysis of the coupled soil–tunnel system. Numerical predictions were compared to the experimental data to validate the effectiveness of the numerical modelling. The interpretation of both experimental and numerical results revealed, among other findings: (a) a rocking response of the model tunnel in addition to racking; (b) residual earth pressures on the tunnel side walls; and (c) residual internal forces after shaking, which are amplified with the tunnel's flexibility. Finally, the calibrated numerical models were used to validate the accuracy of simplified design methods used in engineering practice.