Paper No.: 0317 LATERAL SPREADING DURING CENTRIFUGE MODEL EARTHQUAKES

Lateral spreading of gently-sloping deposits of liquefiable sand is a cause of much damage in earthquakes, reportedly more than any other form of liquefaction-induced ground failure. Estimation of the forces induced on structures such as pile foundations within these deposits requires a knowledge of both the magnitude of spreading occurring and the distribution of displacement through the liquefied layer. This paper concerns itself with measuring the displacement profile through a laterally spreading slope by means of coloured sand marker lines within centrifuge models. A series of dynamic centrifuge model tests have been carried out on gently sloping sand beds containing instrumentation for measuring pore pressures, accelerations and displacements. The results of these experiments are presented in the paper. It can be concluded that the surface displacements relatively easily measured in the field by such techniques as aerial photogrammetry do not necessarily indicate the magnitude of lateral spreading occurring at depth. Surface layers above the phreatic surface may rotate, causing increased displacement with depth. Alternately they may shear on the boundary with the underlying liquefied layer by virtue of support received from the toe, giving a displacement discontinuity