Geotechnical investigations at three sites in the South Carolina Coastal Plain that did not liquefy during the 1886 Charleston earthquake.

摘要

Geotechnical investigations were performed at three sites in the South Carolina Coastal Plain where liquefaction is believed to not have occurred in 1886 or during other Holocene earthquakes. The three sites are the Coastal Research and Education Center (CREC) located near Charleston, and the Borrow Pit and Marsh Road sites at Hobcaw Barony near Georgetown. The investigations consisted of nine seismic cone penetration test (SCPT) soundings, three non-seismic cone penetration test (CPT) soundings, one standard penetration test (SPT) boring, and two dilatometer test (DMT) soundings. Shear wave velocities ( Vs) were calculated from the SCPTs using pseudo interval measurements at the CREC site and true interval measurements at the two Hobcaw Barony sites. The SPTs were performed with hammer energy measurements so the most accurate corrected blowcounts (N1) 60 could be obtained. The at rest lateral earth pressure coefficients (Ko) were estimated from the DMT measurements.; It was determined that thick medium dense surficial sand deposits exist at each site. These near-surface deposits (below the ground water table) have average normalized cone tip resistance (qt1N) values ranging from 95 to 139 and stress-corrected shear wave velocity ( Vs1) values between 230 and 296 m/s. Values of Ko for the near-surface sand deposits at the CREC site and the Borrow Pit site average 0.9 and 0.7, respectively.; Measured values of Vs from the SCPTs were compared with predicted values of Vs based on the empirical relationships by Andrus et al. (2007). At the three sites the measured to predicted Vs ratios (MPV sR) are 1.38, 1.47 and 1.45, respectively. For the CREC site the value of 1.38 is practically the same as the MPVsR determined by Hayati and Andrus (2008) for the 100,000 year old Wando Formation in Charleston, which did not liquefy during the 1886 earthquake. The Borrow Pit site and the Marsh Road site have similar MPVsR values, indicating the thick sand layer at these sites are similar in age (about 200,000 years old). These MPVsR values support the belief that liquefaction did not occur at the three sites during the recent past.