Liquefaction Evaluation by Seismic Potential Procedure

Von Thun, J. Lawrence; Wilson, John A.; ,

Liquefaction Evaluation by Seismic Potential Procedure

by J. Lawrence Von Thun, U.S. Bureau of Reclamation, Boise, United States,
John A. Wilson, U.S. Bureau of Reclamation, Boise, United States,

Document Type: Proceeding Paper

Part of: Geotechnical Practice in Dam Rehabilitation

Abstract:

Empirical procedures in common use for liquefaction evaluation employ information from a variety of sources in order to evaluate whether or not a site will undergo liquefaction. The information sources include in situ testing, earthquake attenuation relationships, laboratory testing, dynamic response estimates, and the historical record of sites that did and did not liquefy. These procedures routinely apply numerous correction factors throughout the process to adjust for variations in field test procedures, depth of overburden, in situ stresses, fines content and many other factors. Although these methods are described as empirical, they are, in fact, based on a combination of empirical data, laboratory test data, and analytical methods. The results in the end can be greatly influenced by the effect of correction factor adjustments. A direct empirical procedure based only on historical observations of liquefaction and the magnitude and distance of earthquakes producing the liquefaction is described. The data base for the empirical procedure used in the past came primarily from Western United States, Chinese and Japanese records. The fit of additional events to the relationship as developed by Ambraseys (1988) is examined as well as the applicability of its use for Eastern United States events. The empirical relationships for seismic potential liquefaction evaluation have been used by the Bureau of Reclamation for several years in the evaluation of the safety of existing dams. This procedure can be effectively applied in locations of low to moderate seismic potential. In such areas, the method can be used to indicate whether or not the seismic potential for liquefaction is indicated as possible for the design earthquake magnitude and distance. The boundary between liquefaction and no liquefaction in the historical record can be interpreted to represent liquefaction occurrence for very loose soils. The use of this interpretation along with discussions of the applications and limitations of the procedure is provided in the paper.

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