Experimental Study on Sliding at the Soil-Structure Interface of a Shallow Foundation

The interaction between a foundation and its supporting soil involves several different energy dissipation mechanisms. For example, sliding of a foundation element is a soil-structure interaction component that can alter the seismic demand on a foundation as well as its superstructure. Experimental data from tests with realistic boundary and stress conditions is required to characterize the frictional properties at the soil-foundation interfaces in order to model sliding of shallow foundations. To this end, a series of large-scale monotonic laboratory shear tests were performed to study the interface between a shallow concrete foundation element and Ottawa F-55 sand under varying normal pressures, shearing rates, and foundation surface roughnesses and textures. The soil-foundation interface behavior was evaluated through a combination of global measurements of force and displacement, as well as by capturing the localized effects around the interface. This article describes the dependency of the interface behavior on each of the aforementioned variables. The results indicate that when subrounded fine sand comes into contact with surfaces of varying roughness, it exhibits different shear resistance behaviors. The findings further reveal insights into the dependency of the interface frictional characteristics and shear failure zone on the real area of contact, which includes irregularities on the surface. The data further utilized to study the impact of adopting different interface friction assumptions on the finite element model’s interface shear response being subjected to monotonic loading. Using the internal friction angle, or a factored down value, as an estimation for interface friction may lead to an erroneous or unconservative prediction of the superstructure response.