Liquefaction

Liquefaction is a geotechnical phenomenon in which saturated soil loses strength and stiffness as a result of increased pore water pressure generated by dynamic loading, such as earthquake shaking. This temporary reduction in effective stress causes the soil to behave like a liquid rather than a solid. Liquefaction most often affects loose to moderately dense, saturated granular soils, especially sands and silts with relatively high water content and limited drainage.

During strong shaking, grains rearrange and pore water is forced upward, increasing pore pressure while decreasing effective stress. When the pore pressure approaches the confining stress, the soil loses shear strength and strain can accumulate as a viscous flow. The effects can include ground settlement, lateral spreading, ground cracks, and surface phenomena such as sand boils or vents. Buried utilities, foundations, and structures can suffer heavy damage due to uneven settlement or loss of bearing capacity.

Assessment and mitigation: Susceptibility is evaluated with in-situ tests (Standard Penetration Test, cone penetration tests) and laboratory cyclic tests that compare cyclic stress ratio to the soil’s cyclic resistance ratio. Critical factors are initial soil density, depth to groundwater, and soil type. Mitigation strategies include improving drainage (vertical drains, dewatering), soil reinforcement or replacement, vibro-replacement or stone columns, preloading and compaction, and the use of deep foundations or structural design measures to accommodate deformations.

History and significance: Liquefaction was first widely documented in major earthquakes and remains a key consideration in seismic risk assessment and geotechnical design.