A theoretical and experimental investigation into the dynamic behaviour of soils
The dynamic properties of 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. The comparison indicates that the properties of dry sand are independent of frequency, while those of fluid saturated sand are sensitive to the viscosity of the fluid and therefore to the frequency of oscillations. A 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 is correctly shown to be asymmetric and the reduction in the resonant frequency with increasing strain amplitude is also correctly represented. The model has been used to generate a series of design curves that allow the dynamic behaviour of foundations to be predicted. Two design examples are given; an offshore gravity structure and a radar installation. The input parameters are based on a hyperbolic shear stress-shear strain equation for the soil. The practical consequences of these findings are assessed with regard to soil testing procedures and dynamic analyses of foundations.