Development of a liquefaction hazard screening tool for caltrans bridge sites

We have developed a liquefaction hazard screening tool for the California Department of Transportation (Caltrans) that is being used to evaluate the liquefaction hazard to approximately 13,000 bridge sites in California. Because of the large number of bridge sites to be evaluated, we developed a tool that makes use of parameters not typically considered in site-specific liquefaction investigations. We assessed geologic, topographic, seismic hazard, and subsurface conditions at about 100 sites of past liquefaction in California. Among the parameters we found common to many of these sites are: (a) low elevations, (b) proximity to a water body, and (c) presence of geologically youthful deposits or artificial fill materials. The nature of the study necessitated the use of readily available data, preferably datasets that are consistent across the state. The screening tool we provided to Caltrans makes use of the following parameters: (1) proximity to a water body, (2) whether the bridge crosses a water body, (3) the age of site geologic materials and the environment in which the materials were deposited, as discerned from available digital geologic maps, (4) probabilistic shaking estimates, (5) the site elevation, (6) information from available liquefaction hazard maps [covering the 9-county San Francisco Bay Area and Ventura County] and California Geological Survey (CGS) Zones of Required Investigation. For bridge sites at which subsurface boring data were available (from CGS' existing database), we calculated Displacement Potential Index values using a methodology developed by Allison Faris and Jiaer Wu. Caltrans' staff will use this hazard-screening tool, along with other tools focused on bridges and foundations, to prioritize site-specific investigations. ?? 2009 ASCE.