Role of input motion in excess pore pressure generation in dynamic centrifuge modelling

Dynamic centrifuge testing is widely used to model geotechnical earthquake engineering problems. This is especially helpful in generating data to validate numerical models or to understand failure mechanisms in a given boundary value problem. The input motions used in many of these tests to simulate the earthquake loading vary from simple sinusoidal motions at a single frequency to more realistic earthquake motions recorded in previous earthquakes. These realistic earthquakes normally contain different amplitude cycles as well as different frequency components. This paper investigates the effect of choice of input motion on the behaviour of loose, saturated soil layers in terms of excess pore pressure generation and settlement. It presents results from centrifuge tests carried out using specially designed input motions that are comparable, with either uniform or non-uniform amplitude cycles. It will be shown that both these types of motions resulted in very similar peak excess pore pressures. However non-uniform amplitude cycles resulted in large, dilation induced suction spikes that can have an effect on accumulated soil deformation. It is concluded that choice of input motion may depend on the type of problem being investigated and the purpose of centrifuge testing.