Soil liquefaction

Soil liquefaction is the loss of strength and stiffness in saturated, loose soil when rising pore-water pressure reduces effective contact between particles, often during earthquake shaking.

Effective stress: The stress carried by a soil skeleton after pore-fluid pressure is subtracted from total stress. Liquefaction weakens soil by reducing the effective stress carried at particle contacts.
Saturated soil: Soil whose pore spaces are filled with water. Liquefaction requires pore water to transmit pressure through the soil skeleton.
Standard Penetration Test: An in-situ test that estimates soil resistance by counting hammer blows needed to drive a sampler. Corrected blow counts help estimate a soil layer's resistance to earthquake-triggered liquefaction.
1964 Niigata earthquake: A magnitude 7.5 earthquake that struck Niigata, Japan, on June 16, 1964. Liquefaction toppled apartment blocks and transformed understanding of earthquake-related ground failure.
Cyclic mobility: A cyclic deformation mode in dense or dilative soil that produces large strains without sustained zero effective stress. It can resemble liquefaction damage but differs in how effective stress evolves during shaking.
Pore-water pressure: The pressure exerted by water within the voids of soil or rock. Its rapid increase during shaking drives the loss of soil strength.
Relative density: A measure of how densely a granular soil is packed relative to its loosest and densest states. Loose granular soil is more prone to contract and build excess pore pressure.
Cone penetration test: An in-situ test that pushes an instrumented cone into soil to measure penetration resistance and pore pressure. Its continuous measurements help identify susceptible layers and estimate triggering resistance.
1964 Alaska earthquake: A magnitude 9.2 earthquake that struck southern Alaska on March 27, 1964. Liquefaction and related ground failures damaged ports, railways, and communities.
Flow liquefaction: A sudden flow failure in which liquefied soil moves under sustained static shear stress. It is a specific, potentially catastrophic form of liquefaction-driven ground movement.

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