What type of foundation is most susceptible to liquefaction?

The most susceptible type of foundation to liquefaction is a spread footing on saturated loose sand. Liquefaction occurs when saturated, loose, and unconsolidated granular soils, such as sand, lose their strength and behave like a viscous fluid during seismic events or other dynamic loading scenarios.

In the case of spread footings on saturated loose sand, the water content and structure of the soil play a crucial role. When an earthquake produces shaking, the pore water pressure in the loose sand increases, which can reduce the effective stress within the soil to near zero. This transformation leads to a state where the soil can no longer support loads effectively, causing structures supported by such foundations to settle, tilt, or even fail entirely.

In contrast, other foundation types mentioned are less vulnerable. Spread footings on dense gravel are typically stable due to the densified state of the gravel, which offers greater resistance to liquefaction. Pile shafts in solid rock are anchored in firm material that does not liquefy, thus providing an extremely stable foundation. Continuous footings on stiff clay are also more resistant since clay tends to have a cohesive structure, which is less susceptible to liquefaction effects compared to loose, saturated sands. Therefore, the nature of the