Use of the mini-cone penetrometer for evaluating the liquefaction potential of sands associated with Charleston, S.C. seismic events

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Virginia Tech

First-hand reports on the 1886 Charleston earthquake contain numerous accounts for the widespread occurrence of liquefaction related features in and near the meizoseismal zone. Recent geologic studies have found evidence for the repeated liquefaction of sandy soils in the Charleston area due to recurring large seismic events. In the course of this investigation 24 mini-cone penetration tests were performed at seven sites in or near the meizoseismal zone of the 1886 earthquake to determine the factors influencing ground failures due to liquefaction. These tests were supplemented with soil borings, sieve tests and a limited number of standard penetration tests to aid in characterization of the sandy soils. Additionally, soil boring records in Charleston were obtained which provided in-situ testing data in an area with documented historical damage. The range of sites at which testing was done, or information was available, represent locations experiencing various levels of liquefaction and distances from the zone of seismic energy release.

Penetration data were used to evaluate resistance of the sandy soil to cyclic loading and fonned the basis for assessing the effects that the lateral extent and distribution of loose sand layers has on the surficial manifestation of liquefaction. With the absence of cementation and extensive soil development, soils as old as late Pleistocene age have been found to be very susceptible to liquefaction. At several sites these soils have undergone at least three episodes of liquefaction and presently exhibit low penetration resistances, indicating that the progressive densification of a liquefiable soil layer can be minor unless it is in very close proximity to a large venting feature. The size and density of occurrence of vents and sand blows has been found to be primarily dependent on the extent of both the liquefiable layer and any overlying resistant layers. Layered system relations utilized with field performance data, and historical and geologic evidence for the occurrence of liquefaction features to suggest that the near surface peak horizontal accelerations induced by the 1886 earthquake were approximately O.3g in the meizoseismal zone and O.2g in the city of Charleston. This is in contrast with previous estimates of seismic shaking all of which point toward values in the range of 0.5 to O.6g. The reason for the different acceleration estimates is not clear at this time, and will be further studied in future extension of this work.