Liquefaction Sites, Imperial Valley, California

Abstract

Sands that did and did not liquefy at two sites during the 1979 Imperial Valley, Calif., earthquake (ML=6.6) are identified and their properties evaluated. From cone soundings, stratigraphy was determined, soil types and properties estimated, and optimal locations for samples and SPT tests selected. Samples were used to classify sediments and to identify modes of deposition. SPT tests were used to evaluate liquefaction susceptibility. Loose fine sands in an abandoned channel liquefied and produced sand boils, ground fissures, and a lateral spread at the Heber Road site. Evidence of liquefaction was not observed over moderately dense over‐bank sand east of the channel nor over dense point‐bar sand to the west. Standard analyses predict that both the channel and the over‐bank sands are liquefiable, but that the point bar is resistant. At the River Park site, a layer of loose floodplain silty sand overlies a layer of clay, which in turn overlies a thick bed of sand that increases in density with depth. Parts of both the upper silty sand and lower sand liquefied and produced hundreds of sand boils. Standard analyses predict that the looser parts of both layers are liquefiable.