On the mechanics of failure of pile-supported structures in liquefiable deposits during earthquakes

Piles are long, slender members inserted deep into the ground to support heavily loaded structures such as bridges, buildings, jetties or oil platforms, where the ground is not strong enough to support the structure on its own. It is not an overstatement to state that most small to medium span river bridges and most G + 4 buildings are supported on piles. In seismic-prone zones, in areas of loose to medium dense sand, where the groundwater table is near the ground surface, piles are also used to support structures such as buildings and bridges. Under moderate to strong shaking, loose to medium dense, saturated, sandy soil liquefies and behaves like a 'solid suspension' due to the rise in pore water pressure. In other words, the sand behaves like 'quick sand' and cannot bear any load. These soils are termed as 'liquefiable deposits' and the phenomenon is termed as 'liquefaction'. Collapse and/or severe damage to pile-supported structures is still observed in liquefiable soils after most major earthquakes. Therefore, this still remains a great concern to the earthquake engineering community. This article explains the mechanics behind the failure of these structures.