How can soil liquefaction damage an earthfill dam during an earthquake?

Soil liquefaction poses a significant risk to earthfill dams, particularly those constructed using hydraulic fill technology.1

During an earthquake, seismic vibrations cause water-saturated, unconsolidated soils to lose their internal strength and behave like a viscous liquid. In an earthfill dam, this process occurs when earthquake shocks cause the water-filled pore spaces between soil grains to collapse. This collapse increases the water pressure between the grains, allowing them to move freely and significantly reducing the soil's resistance to shear stress.2

Because hydraulic fill dams retain large quantities of water within their soil structure, they are especially vulnerable to this phenomenon. When the soil liquefies, it loses its ability to support the structure, which can lead to the "slipping" of the fill material and, in severe cases, partial or total collapse of the dam. A notable example of this failure occurred during the 1971 earthquake in Los Angeles, when the Van Norman Dam suffered a partial collapse due to the liquefaction of its hydraulic fill.12