Abstract：Confining pressure is one of the key factors that affect dynamic soil properties such as low-amplitude shear modulus and damping ratio，normalized modulus reduction and material damping curves，etc.. By analyzing the classical model of dynamic soil properties，predictive equations for estimating low-amplitude shear modulus and damping ratio are presented. Based on the study of M. B. Darendeli，a simple method for calculating normalized shear modulus reduction and damping ratio curves is proposed under certain effective confining pressure from those under referenced confining pressure. According to this method，assuming that the confining pressure has little influence on the shape of the curves；the curves under certain confining pressure can be easily obtained by changing the strain value of the reference curves. The key parameter in this method is deduced with regression analysis of laboratory data collected from various sources. The predicted dynamic shear modulus reduction and damping ratio curves are in excellent agreement with those of the empirical models and test results. Because the strain dependency，the proposed method can be easily combined to the equivalent linear method programs such as DYNEQ for seismic site response analysis. Case study shows that it is reasonable to use effective mean confining pressure dependent soil properties to calculate the surface response spectrum of deep site from rock response spectrum under major earthquake.
