What is liquefaction in soil mechanics?

Liquefaction in soil mechanics refers to the phenomenon where saturated soil substantially loses strength and stiffness in response to applied stress, often during an earthquake or other rapid loading conditions. This loss of strength occurs due to the buildup of pore water pressure within the soil, which reduces the effective stress and leads the soil to behave more like a liquid than a solid.

In cases where the saturated granular soil experiences cyclic loading, such as during seismic events, the grain-to-grain contact forces can be disrupted, resulting in a sudden and significant reduction in shear strength. The soil can then flow under its own weight, potentially leading to severe ground deformation, loss of bearing capacity for structures, and even completion of landslides.

The other choices do not accurately describe liquefaction. A gradual increase in soil strength would refer to processes such as consolidation or compaction, which are opposite to what occurs during liquefaction. The idea of soil drying out relates to desiccation or shrinkage, which is also not directly related to the loss of strength under saturation. Lastly, while liquefaction can contribute to erosion in some cases, it primarily describes the dramatic and sudden drop in shear strength attributed to pore pressure changes rather than the erosion itself.