Characterizing the dynamic properties of South Carolina soils for ground motion evaluation

The South Carolina Coastal Plain is one of the most seismically active regions in the eastern U.S. Dynamic soil properties, which include small-strain shear-wave velocity, VS, and the variations of shear modulus and material damping with shear strain, are required inputs for earthquake ground motion and site response analysis. In this study, a database of available soil properties is compiled to develop procedures for characterizing the dynamic properties of South Carolina soils.; The database includes 89 VS profiles from the greater Charleston area. Average shear-wave velocities in the upper 30 m are calculated for many of the profiles. If the 89 profiles can be considered representative, about 98% of the greater Charleston area is NEHRP site class D and E, assuming no special site class F exist. Many of the profiles are further broken down and separated based on subsurface geology to characterize the VS properties of six major units.; Predictive equations for estimating normalized shear modulus, G/Gmax, and material damping ratio, D, of Quaternary soils, Tertiary and older soils, and Residual/Saprolite soils are developed using laboratory test results for 122 specimens and assuming a modified hyperbolic model. The D equations are expressed in terms of a polynomial function of G/Gmax plus a minimum damping ratio. In general, the Quaternary soils exhibited more linearity than the other two older soils with similar PI. Comparisons between the recommended and earlier curves show that the influence of PI is not as significant as previously suggested.; The recommended G/Gmax equations involve no significant bias. Bias related to the D equations at values greater than 2.0 are less than 12%. Procedures to estimate model uncertainty associated with the recommended equations at any given condition are developed using the point estimate method.; A case study is provided to illustrate application of the recommended procedures. Effects of several parameters on the response spectra are assessed.; The results of this study provide important required inputs for site-specific response analysis and detailed seismic hazard zonation in South Carolina. Some of the results may be useful for other areas with similar soil conditions.