The dynamic behaviour of saturated and unsaturated sand and the liquefaction potential

Much progress has in recent years been made to develop procedures for evaluating the possibility of liquefaction of sands during earthquakes or other types of cyclic loading. A basic feature has been the assumption that during shaking there would be no significant dissipation of pore water pressures so that the undrainded state would be applicable. The purpose of the research was to investigate the dynamic behaviour of saturated and unsaturated sand. The unsaturated sand was investigated in terms of changes in shear moduli and damping ratio, whilst the mechanism of pore pressure buildup and dissipation of saturated sand was monitored. Samples of the Koeberg Nuclear Power Station were tested with the resonant column device at high and low amplitude shearing strains and varying confining pressures. The liquefaction potential of the sand was tested by means of the cyclic triaxial test and the torsional simple shear device. The post cyclic dissipation of pore pressures was also monitored.