Normalized Shear Modulus and Material Damping Model for Southeastern US Residual Soil and Saprolite

This paper presents the development of a new normalized shear modulus and material damping model for southeastern US residual soil and saprolite. The model is based on other investigators' resonant column and torsional shear tests on 39 specimens obtained from Alabama, North Carolina, South Carolina, and Virginia. The normalized shear modulus relationship is established using a modified hyperbolic model and regression analysis. The material damping relationship is developed considering the small-strain linear damping and the medium- to large-strain nonlinear damping separately. It is found that the plasticity index and confining stress are the two most significant variables in modeling the normalized shear modulus. It is also found that the compiled linear damping values are weakly correlated with confining stress and plasticity, and the nonlinear damping is adequately modeled using a parabolic function of normalized shear modulus. The new model is partially validated using data not considered in the modeling. A procedure is summarized for validating/correcting the implied dynamic peak shear strength of normalized shear modulus curves at strain levels greater than 0.2%, beyond the test data range. The study is part of an effort to develop site adjustment factors compatible with newly developed statewide seismic hazard maps for the state of South Carolina.