Subsidence of Building Foundation Resting Upon Liquefied Subsoil: Case Studies and Assessment

Subsidence and tilting of such structures as oil storage tanks and buildings which are not supported by deep foundations are an important kind of damage induced by seismic soil liquefaction. The present paper describes the results of case-history studies conducted in Dagupan City in the Philippines, where substantial damage occurred to buildings during an earthquake in 1990. Relationships of size and shape of buildings with the extent of subsidence were found, while a better correlation was detected by using soil stratification. This correlation appears helpful for quick assessment of the liquefaction-related risk of buildings. To investigate further the mechanism of subsidence, shaking table tests were conducted. Thereafter, an analytical method for predicting the subsidence of a building was developed by considering liquefied subsoil as a viscous fluid. It was accordingly possible to obtain reasonable matching between calculated and observed subsidence when the extent of damage was significant. On the other hand, a relatively poor matching when the damage extent was light suggests that liquefied sand was not so soft as supposed in the analysis. Combining the aforementioned correlation with stratification, this analytical measure will help carry out the risk assessment of liquefaction-prone buildings.