Aging Factors for the Cyclic Resistance Ratio of Pleistocene Sands from the South Carolina Coastal Region

Abstract

Laboratory and field tests were performed on sandy soils from six Pleistocene-age sites in the South Carolina coastal region to investigate the age-related resistance to liquefaction. Stress-controlled cyclic triaxial tests were used to determine the cyclic strength of soils with geologic ages ranging from approximately 59,000 to 1,200,000 years. Three sites have evidence of liquefaction in the form of sand blows that are 467 to 4,185 years old as determined from C14 dating of embedded organic material. The other three sites show no indications of liquefaction. Cyclic stress ratios ranging from 0.095 to 0.225 were applied to undisturbed and reconstituted soil specimens that were consolidated to an effective stress equal to 100 kPa. Soil specimen liquefaction was defined to occur when the excess pore pressure was equal to the confining effective stress. Estimates of the at-rest earth pressure coefficient were determined using measurements from the flat plate dilatometer and the cone penetrometer and were applied to the laboratory cyclic stress ratio occurring at the 15th loading cycle to determine the laboratory–field equivalent cyclic resistance ratio. The age-dependent liquefaction resistance was determined using additional data from the inner coastal plain of South Carolina and assessing the cyclic resistance ratios and their associated KDR ratios relative to the base data and applying one of the more recently developed liquefaction triggering model. It was found that the development of the aging factor should be independent of the liquefaction triggering model. Subsequently, the aging factor is developed using an offset that is constrained at 20 years and a KDR=1.0, and was found to range from 1.00 at 20 years to 1.45 at 1.0 Ma for the original deposition ages of the soils and 1.00 at 20 years to 1.51 at 1.0 Ma for the data set consisting of the last disturbance and original deposition ages of the soils.