Liquefaction evaluation guidelines for practicing engineering and geological professionals and regulators

Liquefaction is a seismic hazard that must be evaluated for a significant p ercentage of the developable areas of California. The combination of the pr esence of active seismic faults, young loose alluvium, and shallow ground w ater are the ingredients that could result in the occurrence of liquefactio n in many areas of California. These ingredients are also found in other se ismically active areas of the United States and the world. The state of Cal ifornia, through the Seismic Hazards Mapping Act of 1990, has mandated that liquefaction hazard be determined for new construction. On a parallel trac k, the Uniform Building Code, since 1994, has provisions requiring the dete rmination of liquefaction potential and mitigation of related hazards, such as settlement, flow slides, lateral spreading, ground oscillation, sand bo ils, and loss of bearing capacity. Fortunately, the state of knowledge has now evolved to where there are field exploration methods and analytical tec hniques to estimate the liquefaction potential and the possible consequence s arising from the occurrence of liquefaction. There are some areas that st ill need further research. Mitigation for liquefaction has become more comm onplace and confidence in these techniques has been increased based on the relatively successful performance of improved sites in the past several maj or earthquakes. Unfortunately, not all practicing engineering and geologica l 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 professional s and building officials, based on California's experience with the current practice of liquefaction hazard analysis and mitigation. Although the guid elines reported in this paper were written specifically for practice in Cal ifornia, it is believed that guidelines can benefit practitioners to evalua te liquefaction hazard in all seismic regions.