Liquefaction is a seismic hazard that must be evaluated for a significant percentage of the developable areas of California. The combination of the presence of active seismic faults, young loose alluvium, and shallow ground water are the ingredients that could result in the occurrence of liquefaction in many areas of California. These ingredients are also found in other seismically active areas of the United States and the world. The state of California, through the Seismic Hazard Mapping Act of 1990, has mandated that liquefaction hazard be determined for new construction. On a parallel track, the Uniform Building Code, since 1994, has provisions requiring the determination of liquefaction potential and mitigation of related hazards, such as settlement, flow slides, lateral spreading, ground oscillation, sand boils, and loss of bearing capacity. Fortunately, the state of knowledge has now evolved to where there are field exploration methods and analytical techniques to estimate the liquefaction potential and the possible consequences arising from the occurrence of liquefaction. There are some areas that still need further research. Mitigation for liquefaction has become more commonplace and confidence in these techniques has been increased based on the relatively successful performance of improved sites in the past several major earthquakes. Unfortunately, not all practicing engineering and geological professionals and building officials are knowledgeable about the current state-of-practice in liquefaction hazard analysis and mitigation. Thus, it was considered necessary to develop a set of guidelines to aid professionals and building officials, based on California's experience with the current practice of liquefaction hazard analysis and mitigation. Although the guidelines reported in this paper were written specifically for practice in California, it is believed that guidelines can benefit practitioners to evaluate liquefaction hazard in all seismic regions.

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