Bearing capacity of embedded and skirted E-shaped footing on layered sand

Abstract

Purpose: The purpose of this study is to investigate the ultimate bearing capacity of the embedded and skirted E-shaped footing resting on two layered sand using finite element method. The analysis was carried out by using ABACUS software. Design/methodology/approach: The numerical study of the ultimate bearing capacity of the embedded and skirted E-shaped footing resting on layered sand and subjected to vertical load was carried out using finite element analysis. The layered sand was having an upper layer of loose sand of thickness H and lower layer was considered as dense sand of infinite depth. The various parameters varied were the friction angle of the upper (30° to 34°) and lower (42° to 46°) layer of sand, the skirt depth (0B, 0.25B, 0.5B and 1B), the embedment depth (0B, 0.25B, 0.5B and 1B) and the thickness (0.5B, 2B and 4B) of the upper sand layer, where B is the width of the square footing. Findings: The ultimate bearing capacity was higher for the skirted E-shaped footing followed by embedded E-shaped footing and unskirted E-shaped footing in this order for all combinations of variables studied. The improvement in the ultimate bearing capacity for the skirted E-shaped footing in comparison to the embedded E-shaped footing was in the range of 0.31 % to 61.13 %, 30.5 % to 146.31 % and 73.26 % to 282.38% corresponding to H/B ratios of 0.5, 2.0 and 4.0 respectively. The highest increase (283.38 %) was observed at φ1 =30° and φ2 =46° corresponding to H/B and Ds/B ratio of 4.0 and 1.0 respectively while the increase was lowest (0.31 %) at φ1 =34° and φ2 =46° at H/B ratio of 0.5 and Ds/B ratio of 0.5. For the skirted E-shaped footing, the lateral spread was more as in comparison to the embedded E-shaped footing. The bearing capacity of the skirted footing was equal the sum of bearing capacity of the surface footing, the skin resistance developed around the skirt surfaces and tip resistance of the skirt with coefficient of determination as 0.8739. The highest displacement was found below the unskirted and embedded E-shaped footing, and at the skirt tip in the case of the skirted E-shaped footing. Further, the displacement contours generated supports the observations of the multi-edge embedded and skirted footings regarding the ultimate bearing capacity on layered sands. Research limitations/implications: The results presented in this paper were based on the numerical study conducted on E shaped footing made from a square footing of size 1.5 m x 1.5 m. However, further validation of the results presented in this paper, is recommended using experimental study conducted on similar size E shaped footing. Practical implications: The proposed numerical study can be an advantage for the architects designing similar types of super structures requiring similar shaped footings. Originality/value: No numerical study on embedded and skirted E shaped footing resting on layered sand (loose over dense) were conducted so far. Hence, an attempt was made in this article to estimate the bearing capacity of the same footings.