Impact of structural skirt on the bearing capacity of a shallow footing under combined eccentric and inclined loading

Weathered sand normally has a lower shear strength and generally requires additional ground improvement measures to fulfil the required bearing capacity. In situations where ground improvement measures are considered inefficient or restricted due to site conditions, a skirted footing can be used as an effective measure to increase bearing capacity. Additionally, the foundation can also be subjected to load eccentricity and load inclination due to the moment and horizontal forces acting on the foundation, respectively. Under the combined effect of moment and horizontal load, the footing is subjected to an eccentrically inclined loading condition, which in turn reduces the ultimate bearing capacity. However, there is a lack of research work on the impact of combined (vertical, horizontal and moment) load on a skirted square foundation. The present work provides laboratory test results on a skirted square (B = 0.1 m) model footing in dense and medium-dense sand. The footing with skirt length varying from L/B = 0 to 1 is subjected to a combined load eccentricity (e) and inclination (a). The load eccentricity varied from e/B = 0 to 0.15, and load inclination varied from 0⁰ to 15. In addition to laboratory tests, finite element analysis was conducted on a prototype footing (B = 1 m) to compare with the laboratory test results. The results indicate that for any combination of e/B and a, the bearing capacity of a skirted footing improved with an increase in skirt length ratio (L/B) compared to a spread footing (L/B = 0). The improvement is found to be 3.7 times in dense soil and 4 times in medium dense soil with L/B = 1 and for the loading at e = 0, a = 0. The improvement factor increases for the case of e > 0, a > 0. A chart has been provided based on laboratory tests and finite element result to estimate the ultimate bearing capacity of skirted footing under combined loading conditions.