Seismic Response Analysis of Quasi-Saturated Saturated Soil Site under Plane P-Wave Incidence

In order to explore the difference of site seismic response between quasi-saturated soil layer and saturated soil layer under elastic wave incidence, based on the theory of quasi-saturated porous media, the dynamic response of quasi-saturated soil foundation overlying bedrock layer is studied. By establishing the mathematical model of quasi-saturated porous medium and single-phase elastic medium, the seismic response of quasi-saturated soil foundation site is analyzed. The governing equations of the quasi-saturated soil layer are derived by using the Biot theory, and the potential function expression of the wave field is obtained by combining the Helmholtz vector decomposition principle. The correctness of the model is verified by numerical examples, and the effects of saturation, porosity, permeability coefficient, viscosity coefficient, stiffness ratio and incident angle on the surface movement of the saturated soil foundation are discussed in detail. The results show that the existence of gas phase in the quasi-saturated soil layer has a significant effect on the ground motion. The vertical displacement of the surface decreases with the increase of saturation, while the horizontal displacement shows the opposite trend. The surface displacement amplitude is greatly affected by the change of porosity, and the permeability coefficient and viscosity coefficient have little effect on the surface displacement amplitude. It is worth noting that when the saturation Sr = 1, that is, when the quasi-saturated soil foundation degenerates into a saturated soil foundation, the maximum difference between the vertical displacement amplitude corresponding to the saturation Sr = 0.97 reaches 94%, and the horizontal displacement amplitude.