Interaction Effect of Two Closely Spaced Skirted Strip Foundations in Cohesionless Soil Using Upper-Bound Limit Analysis

The bearing capacity of two interacting skirted strip foundations resting on cohesionless soil medium has been determined using upper-bound limit analysis along with a multiblock failure mechanism. The effect of the interaction has been explored by obtaining the variation of the efficiency factor () at different clear spacing (s) between the foundations, the embedment depth of skirts (D-f), and the angle of the internal friction of soil (phi). The bearing capacity of interacting footings was found to be maximum at some critical spacing (s(cr)). Beyond s(cr), the bearing capacity was found to decrease continuously with increases in the spacing and eventually became the same as that of an isolated foundation at maximum spacing (s(max)). The difference between s(cr) and s(max) was found to increase with increases in phi. A detailed parametric study was carried out by varying the clear spacing, the embedment ratio (D-f/B-f), and the soil friction angle. The results obtained from the present theoretical analysis for a single isolated foundation were compared with the available theoretical and experimental data reported in the literature, whereas the present upper-bound efficiency factors for interacting footings were compared with those obtained separately from the finite-element analysis.