Better CE Practice Test

Liquefaction is when saturated soils temporarily lose their ability to carry shear stress because the pore water pressure builds up under dynamic loading, so the effective stress that keeps the soil grains interlocked drops and the soil behaves more like a liquid. In saturated sands, cyclic shaking—such as during an earthquake—causes repeated compression and dilation of the pore space, and the water pressure increases faster than it can drain away. With the effective stress nearly gone, the soil’s shear strength collapses, leading to sudden ground flow, settlements, or lateral spreading. This mechanism is specific to the combination of saturation, cyclic loading, and rapid pore pressure rise. Other possibilities described—strength loss simply from saturation, chemical degradation, or consolidation under static loads—do not capture the dynamic pore-pressure-driven loss of strength that characterizes liquefaction.