APPLICABILITY OF THE SIMPLIFIED THREE-PHASE ANALYSIS TO THE SEISMIC BEHAVIOR OF UNSATURATED LATERALLY LAYERED GROUND

Abstract

 In this research, a series of centrifuge model tests and effective stress analyses was carried out in order to clarify the effect of desaturation on the seismic behavior of horizontally layered ground. In the model tests, unsaturated model ground with the degree of saturation of 90% was created by controlling the water injection speed from the bottom of a rigid box during the saturation process. While the rise in excess pore water pressure in the unsaturated ground was suppressed compared to that in the saturated ground, the excess pore water pressure in the unsaturated ground took more time to be dissipated. In the effective stress analyses, simplified three-phase analyses, where equivalent bulk modulus is used for a mixture of liquid (or pore water) and gas (or pore air) assuming that suction is zero, were also performed in addition to three-phase analyses strictly considering pore water and pore air pressures. The simulation has clarified that the simplified three-phase analyses can be applied to the seismic behavior of unsaturated sandy ground when the degree of saturation is relatively high.