Performance of rocking foundations on unsaturated soil layers with variable groundwater levels

Abstract

An emerging foundation design scheme, termed a rocking foundation, has the potential to limit loads transmitted to the superstructure, with the potential trade-off of increased settlements and rotations at the foundation level. These soil deformations can be significant for foundations with low vertical bearing capacity factors of safety. In this study, a set of dynamic centrifuge tests was performed to assess the response and to develop design considerations for a rocking foundation embedded in soil with varying degrees of saturation. Foundation design procedures dependent on degree of saturation are developed to predict moment capacities and initial rotational stiffness. Experimental data were used to validate the reliability of these procedures, regardless of the degree of saturation in the underlying soil. As the degree of saturation reduced, the moment capacity of the foundation increased, potentially increasing the load transmitted to the superstructure. Further, foundation settlements and rotations in the saturated soils can be reduced by lowering the water table depth in the underlying soil layer, which is beneficial to the performance of rocking foundations. Consequently, the degree of saturation of the supporting soil should be considered in the foundation design to predict the foundation settlement–rotation response and to assess properly the superstructure ductility demands.