CENTRIFUGE MODELING ON MANHOLE UPLIFT IN A LIQUEFIED TRENCH

Abstract

The uplift behavior of sewage manholes due to liquefaction in a trench is investigated through a series of dynamic centrifuge model tests. The objectives of a series of tests are to study the mechanism of the uplift and to obtain relationships among uplift displacement and factors affecting the uplift. The factors considered in the experiments are the ground water levels, the magnitude of input accelerations, the duration time of shaking, the relative densities of trench backfill and the native ground, the material of native ground, the volume of a trench, the apparent unit weight of a manhole, and the contact conditions at the bottom of a manhole. Test results show that the primary cause of uplift is the reduction of the effective confining stress near the bottom of a manhole due to strong shaking. The magnitude of uplift is found to be strongly correlated with the ground water depth, the intensity of shaking, the shear deformation of the trench, and the contact conditions at the bottom of the manhole. These findings are believed to be useful for engineering practice in the mitigation of the manhole uplift.