Large-Scale Shake Table Tests on a Shallow Foundation in Liquefiable Soils

Abstract

The significant damage observed during recent earthquakes resulting from liquefaction of shallow saturated soil deposits beneath structures has illustrated the need for further research in the area of liquefaction-induced ground movement effects. This study used the shake table facility at the University of California, San Diego to evaluate the liquefaction-induced settlement of a shallow foundation founded on top of liquefiable ground conditions. To study the seismic performance of a shallow rigid foundation, two large-scale shake table tests were conducted using different input motions with varying peak accelerations. The experimental model comprised three soil layers and included a shallow foundation seated over an unsaturated crust layer underlain by saturated loose and dense layers. The model ground was based on similar subsurface ground conditions observed in recent earthquakes in New Zealand, Japan, and Turkey. The seismic response of the model foundation and the soil was captured through intensive instrumentation. The main purpose of this study was to better understand the contributing mechanisms in liquefaction-induced settlement of buildings during strong shaking. Results from this series of tests were used to explore different liquefaction mitigation countermeasures; this study served as a baseline for two follow-on shake table tests which are not discussed in this paper. Detailed discussions of the excess pore-water pressure generation and dissipation, and its effect on the contributing mechanisms of liquefaction-induced settlement are presented, along with the application of standardized cumulative absolute velocity as an intensity measure to estimate the amount of liquefaction-induced settlement. The flow velocity calculation due to hydraulic transient gradient indicated an upward flow in the loose layer, which explains the observed sand ejecta. Measured and estimated foundation settlements were compared using simplified procedures. The observed foundation settlement generally was higher than the estimated settlement. This series of large-scale shake table tests provides a unique benchmark for calibration of numerical models, and simplified procedures to reliably estimate liquefaction-induced building settlements. Future mitigation tests can be evaluated using the results of this baseline experimental study.