This paper describes the retesting of liquefaction and nonliquefaction field case histories in the Imperial Valley using the electric cone penetration test (CPT). Subsurface testing of the River Park and Heber Road sites first occurred following the 1979 Imperial Valley earthquake (Bennett et al. 1981, Youd and Bennett 1983). These two sites are rich in information because they have experienced several earthquakes in recent history, have been subjected to moderate levels of strong ground shaking, the liquefiable layers have appreciable fines content, and the sites contain a number of high-quality non-liquefied data points. The recent liquefaction case history database for probabilistic assessment of liquefaction triggering by Moss et al. (2003), is based primarily on data acquired using the modern electric cone following ASTM D5778. Case histories previously explored with a cone not adhering to current ASTM standards may introduce significant epistemic uncertainty into the assessment of liquefaction potential and are considered sub-optimal for probabilistic analysis purposes. This paper describes the acquisition and analysis of modern electric cone data at the Heber Road and River Park sites. These important sites can now be incorporated into the probabilistic CPT-based liquefaction case history database and used for back-analysis of liquefaction triggering. Discussed are the effects of ground motion character and frequency content on liquefaction at these two sites and how this influences the results using a simplified liquefaction procedure.
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