An experimental and theoretical comparison between static and dynamic torsional soil tests

The dynamic properties of dry Leighton Buzzard sand have been investigated using a resonant column test apparatus. These data are compared with very low frequency cyclic tests on identical specimens of sand. The comparison indicates that the properties of dry sand are independent of frequency. A simple one-dimensional model of kinematic hardening plasticity is used to predict the dynamic behaviour of the sand. The input parameters for this model are based on the results of static tests. These may be conducted on standard laboratory equipment with only minor modifications. The predictions are in good agreement with the measured data. In particular, the frequency response close to resonance was correctly shown to be asymmetric and the reduction in the resonant frequency with increasing strain amplitude was also correctly represented. The practical consequences of these findings are assessed with regard to soil testing procedures and dynamic analyses of foundations. Particular emphasis is placed on the dynamic analyses of the foundations for vibrating machinery and offshore gravity structures.