Empirical Methodology to Estimate Seismically Induced Settlement of Partially Saturated Sand

Settlement of soil layers during and after earthquake shaking is a major cause of damage to buildings and geotechnical structures. The available empirical design methods to consider seismically induced settlement focus on sands in dry or water-saturated conditions, and there is currently a gap in the basic understanding of the mechanisms of seismically induced settlements of partially saturated sands. An effective stress-based empirical methodology is proposed to estimate the seismically induced settlement of a free-field layer of sand in partially saturated conditions. This approach estimates the settlement by separately considering the volumetric strains caused by compression of void space during strong shaking (seismic compression) and dissipation of excess pore water pressures generated during earthquake shaking (postcyclic reconsolidation). A parametric evaluation of the methodology indicates that the small strain shear modulus, the parameters of the modulus reduction curve, the approach to estimate the upper bound on volumetric strain during liquefaction, and the pore water pressure generation parameter can have significant impacts on the predicted settlement. The model predictions were validated using results from a newly developed centrifuge physical modeling system that involved the use of steady-state infiltration to maintain a uniform degree of saturation with depth in the sand layer. Both the model and experimental results show a nonlinear trend in surface settlement with degree of saturation, with a minimum value obtained for sand at a degree of saturation between 0.3 and 0.6.