Predicting Vₚ and constrained modulus reduction curve based on Vₛ and shear modulus reduction curve in accordance with poroelastic theory
The compression wave velocity (Vₚ) of sediments plays a key role in seismic wave amplification of vertical motion and is required in site response analysis. However, such information is usually lacking during field exploration (e.g. the surface wave method) because only shear wave velocity (Vₛ) is obtained. This aim of this study is to predict Vₚ based on Vₛ empirically and theoretically, particularly focusing on saturated conditions. The empirical approach is to establish the Vₚ correlation dependency on Poisson's ratio and Vₛ, and the theoretical approach is based on poroelastic theory that accounts for the interaction between fluid and soil skeleton. The engineering geological database for the Taiwan strong motion instrumentation program and the Kiban Kyoshin network database in Japan are adopted to establish an empirical model and validate poroelastic theory. The validated poroelastic approach is used to develop a constrained modulus reduction curve dependency on the porosity, Vₛ, Poisson's ratio and degree of saturation with a shear modulus reduction curve. The proposed approach can be used to develop generic Vₚ profiles and constrained modulus reduction curves for the site response to vertical motion given a site-specific Vₛ profile.