Behavior of Circular Footings Resting on Confined Granular Soil

This paper presents the results of laboratory model tests on the influence of soil confinement on the behavior of a model footing resting on granular soil. Confining cylinders with different heights and diameters were used to confine the sand. The ultimate bearing load of a circular footing supported on a three-dimensional confined sand bed was studied. The studied parameters include the cell height, cell diameter, the depth to the top of the cell, and the embedded depth of footing. Initially, the response of a nonconfined case was determined and then compared with that of confined soil. The results were then analyzed to study the effect of each parameter. The results indicate that the bearing load capacity of circular footing can be appreciably increased by soil confinement. It was concluded that such reinforcement resists lateral displacement of soil underneath the footing leading to a significant improvement in the response of the footing. For small cell diameters, the cell– soil footing behaves as one unit (deep foundation), while this pattern of behavior was no longer observed with large cell diameters. The recommended cell heights, depths, and diameters that give the maximum bearing capacity improvement are presented and discussed.