Liquefaction Hazard

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Liquefaction is a major cause of structural damage during earthquakes. (Liquefaction is a loss of shear strength of soils during strong ground shaking). The accepted procedure for assessing liquefaction hazard is the "simplified procedure for evaluating liquefaction potential" developed by Seed and Idriss. Recent observations indicate that this procedure may overestimate the liquefaction hazard for earthquakes of Richter magnitude 6.5 or less. Since modifications to a design to prevent liquefaction damage are usually expensive, any overestimate of the liquefaction hazard is economically undesirable. The objective of this research program is to examine the hypothesis that the magnitude scaling factors used in this simplified procedure are too small for moderate earthquakes. This objective is achieved by analyzing field performance data, and statistically deriving magnitude scaling factors that are consistent with observed performance. The tasks being addressed include, (1) the analysis of sites where geotechnical data have been collected, and where ground motions have been recorded at or near the site; (2) supplementing these few histories by drilling and testing additional sites where ground motions and past liquefaction behavior are known, and (3) reanalyzing tabulated case histories. This research program is expected to reduce the calculated hazards to a level consistent with observed field behavior, leading to less costly though equally safe design and construction.