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First-hand accounts of sand boils and other liquefaction-related phenomena associated with the Charleston, SC earthquake of 1886 provide clear evidence that liquefaction was common in this event. Recent geologic investigations in the Charleston area have found evidence for the repeated liquefaction of sandy soils in the Charleston area due to recurring large seismic events. Although this information has led to an improved understanding of seismicity in the Charleston region, little hard data exists in terms of ground motion characteristics or levels of seismic loading. A two-year field investigation was undertaken by Virginia Tech to study the liquefaction findings associated with the 1886 event from the perspective of geotechnical engineering. This involved defining the engineering parameters of the Charleston soils on the basis of in-situ and laboratory tests, and estimating the levels of seismic loading required to produce the observed liquefaction phenomena. Of the sites where field tests were performed, the surficial soils were largely formed from ancient beach ridge deposits. The findings showed that soil conditions within these deposits are appropriate for liquefaction. Also, there is clear evidence that soils as old as 230,000 years have liquefied multiple times in the past 10,000 years. Many of these soils remain susceptible to liquefaction at relatively low levels of seismic shaking, although there is some evidence for progressive densification. With respect to the seismic loadings, evidence is presented which suggests that both the magnitude and peak acceleration of the 1886 earthquake were less than what has been proposed by the seismological community (M = 7.7 and 0.5 - 0.6g peak acceleration). The findings of this study indicate that for an M = 7.5 event, peak accelerations in the 0.3 to 0.4g range would serve to explain the observed 1886 liquefaction phenomena. If it is assumed that the magnitude of the 1886 earthquake was less than 7.5, then the estimated peak accelerations increase. / Ph. D.

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. / Master of Science