Simplified Equivalent Linear and Nonlinear Site Response Analysis of Partially Saturated Soil Layers

Abstract

Dynamic properties of soils including small-strain shear modulus (Gmax), shear modulus reduction function (G/Gmax), and damping (D) are affected by changes in the degree of saturation. Inter-particle suction forces in partially saturated soils result in higher effective stress values, which in turn, vary the dynamic soil properties. These alterations could lead to different wave propagation mechanisms, acceleration amplification patterns, and seismically induced settlements. This paper aims to identify the challenges involved in nonlinear seismic site response analysis of partially saturated soils by looking at the response of 10-m sand and silt layers with different constant suction profiles. A set of frequency domain equivalent linear and nonlinear site response analysis under scaled Northridge earthquake motion was performed. A modified version of Bishop’s effective stress equation for partially saturated soils has been utilized to calculate the dynamic soil properties (i.e. Gmax, G/Gmax, and D). Specifically, surface-to-base intensity amplifications (Peak Ground Amplifications and Arias Intensities), spectral accelerations, and lateral deformation profiles of the sand and silt layers with different suction profiles were generated and compared. The insight gained from this study was used to plan and design more complex nonlinear Finite Element site response analysis.