Mapping liquefaction potential of aged soil deposits in Mount Pleasant, South Carolina

Liquefaction potential of aged soil deposits in Mount Pleasant, South Carolina, based on the 1886 Charleston earthquake is characterized in this paper. The characterization involves reviewing available first-hand accounts of 1886 ground behavior, analyzing cone penetration test (CPT) and shear wave velocity data, and correlating the results with geology. Careful review of the first-hand accounts reveals that nearly all cases of surface effects of liquefaction can be associated with the younger sand deposits that lie adjacent to the harbor, rivers, and creeks. Only one documented case of minimal surface effect of liquefaction can be definitely associated with the older sand deposits of the 100,000-year-old Wando Formation. Ratios of measured-to-estimated shear wave velocity indicate that the younger sand deposits and the older sand deposits have measured velocities that are 9% and 38%, respectively, greater than 6-year-old sand deposits with the same CPT tip resistance. Liquefaction potential is expressed in terms of the liquefaction potential index (LPI) proposed by Iwasaki and others. LPI values for the Wando sands computed from the CPT profiles are incorrectly high, if no age corrections are applied. If age corrections are applied, computed LPI values match well the observed field behavior in both the younger sands and the older sands. The results are combined with a 1:24,000 scale geologic map to produce a liquefaction potential map of Mount Pleasant. The findings of this study agree remarkably well with a previous liquefaction potential study of aged soil deposits on Charleston peninsula.