Behaviour of Two Closely Spaced Strip Footings Placed on a Stiff Clay Bed under Cyclic Loading

Abstract

Foundations are sometimes placed very close to each other because of space limitations or to limit the footing loads or to accommodate certain structural details. When footings are placed at close spacing, they interact with each other and the behaviour of each individual footing is altered compared to that of a single isolated footing. Also, foundations are often subjected to cyclic live loads in addition to self-weight of the structure causing change in soil performance below it. The design of foundations placed close to each other and subjected to cyclic loading is very complex as both of the phenomena (i.e., footing interference and cyclic load) affects the behaviour of foundation soil. The presence of clayey soil deposits in the construction site adds further uncertainty to this problem because there is no consensus among the researchers regarding interfering footing behaviour on clay. To uncover the actual behaviour of two closely spaced surface strip footings on clay deposits under cyclic loading, small-scale experimental studies with footings placed at two different spacings were carried out in the Civil Engineering laboratory at the University of New South Wales (UNSW@ADFA). The study shows that the application of low-frequency cyclic load improves the bearing capacity and stiffness of foundation soil (clay), irrespective of the interfering footing spacing. Also, the permanent deformation of interfering footings placed at closer spacing is found to be smaller compared to that of footings placed at wider spacing.