Cyclic resistance ratio of pleistocene-age sands from the South Carolina coastal plain

Abstract

Field and laboratory tests were performed on sandy soils from three Pleistocene-age sites in the South Carolina Coastal Plain to investigate the age–related resistance to liquefaction. Reported research indicates that liquefaction resistance of sands increases with the age of the deposit, and that liquefaction may reset the aging clock. The stress-controlled cyclic triaxial test was used to determine the cyclic strength of soil deposits with geologic ages of approximately 200,000, 450,000, and 1,400,000 years and evidence of sand blows that are 467 to 4185 years old. Specimens were obtained using a fixed piston sampler frozen ex situ and include naturally occurring differences in fabric. Cyclic stress ratios ranging from 0.135 to 0.225 were used to determine the peak deviator stress applied during the cyclic triaxial test and were initially estimated from two age-based methods, which were found to over-estimate the laboratory cyclic stress ratio. Estimates of the at-rest earth pressure coefficient were applied to the laboratory cyclic resistance ratio, which resulted in field cyclic resistance ratios that ranged from 0.100 for the oldest deposit (1,400,000 years) to 0.131 for the mid-aged deposit (450,000 years) for initial liquefaction occurring when the generated excess pore pressure was equal to the effective confining stress of 100 kPa (ru = 1.0) at N equal to 15 cycles. The carbon-dated age of the sand blow events correlated with the field cyclic resistance ratios; the geologic ages of the soil deposits did not. A correlation between the clay content, not the fines content, was observed.