Behavior of closely spaced square and circular footings on reinforced sand

This paper describes an experimental investigation conducted to evaluate the ultimate bearing capacity, the settlement and the tilt of two types closely spaced footings, one having square shapes and the other having circular shapes, on unreinforced and reinforced soil. To decrease the objectionable influence of interference on the performance of the closely spaced footings, the foundation soil is reinforced by geogrid layers. The results of this reinforcement show both positive and negative effects, namely, a positive effect because there is a considerable increase in the ultimate bearing capacity, and a negative effect because there is an increase in settlement and tilt. Regarding the experimental results, the negative effect of interference can be decreased considerably through the use of soil reinforcements. The ultimate bearing capacity of the interfering footings increased by about 25–40%, whereas the settlement of the interfering footings at the ultimate load increased in the range of 60–100%. However, the closely spaced footings tilted by approximately 45% and 75% for reinforced sand with one and two layers of geogrid, respectively.