Influence of Footing Size and Matric Suction on the Behavior of Shallow Foundations in Collapsible Soil

Abstract

This work analyses the influence of footing size and soil matric suction on the behavior of shallow foundations on unsaturated sandy soil, in terms of bearing capacity and settlements. Fourteen plate load tests were performed at the Experimental Site of USP/São Carlos. Rigid metal plates were used, with diameters varying between 0.20 m and 0.80 m and reinforced concrete footings, with circular base diameter 1.50 m. All the plates and the footings were installed at a depth of 1.5 m. These tests were conducted either with matric suction monitoring using tensiometers installed at the bottom of the hole or with soil flooding. The important role of the matric suction was confirmed. A reduction of the matric suction close to zero causes a great decrease in the bearing capacity and a significant increase in the settlement. In relation to the footing size (B), the bearing capacity as well as the settlements did not present a constant linear increasing variation. This work also proved the importance of considering the soil collapsibility in unsaturated soil shallow foundations design. When this factor is not considered, the calculated allowable bearing capacity may cause very high settlements if soil flooding occurs.