Interference Effect of Closely Spaced Footings Resting on Granular Fill over Soft Clay

Abstract

In the present paper, the interference effects on bearing capacity and settlement behavior of two closely spaced identical footings resting on the surface of granular fill (sand layer) of limited thickness underlain by soft clay have been studied by laboratory model tests. Three pairs of model footings with different shapes are used to study the effect of the aspect ratio of footing on footing interference. The width (B) and length (L) of the footings are selected in such a way that the aspect ratio or L:B ratio of the footings is varied as 1.0 (square), 1.5 (rectangular), and 2.0 (rectangular). Results show that the maximum interference factor for closely spaced footings on a single-layer sand bed is 40% higher in magnitude compared with the sand-clay layered soil bed or homogeneous clay bed. Furthermore, the interference factors increase with the increase in the L:B ratio of the footings. The optimum spacing ratio is independent of the L:B ratio of the footings, and it is 1.5 times the width of the footings. Based on the load-spread mechanism and the deformation of sand-clay interface, an analytical solution has been proposed to determine the bearing capacity of two closely spaced rectangular footings.