Vol. 2 No. 3 (2026) Cover Image
Vol. 2 No. 3 (2026)

Published: September 30, 2026

Pages: 52-64

Research Article

Influence of Skirt Length and Foundation Size on the Bearing Capacity of Circular Foundations Resting on Sandy Soil

kawther yaly Hussain Al-Soudany 1 Nahla M. Salim 2 Luay Y. Hussein 1
1 College of Engineering, University of Technology-Baghdad, Baghdad, Iraq
2 Department of Civil Engineering, College of Engineering, Al-Naji University, Baghdad, Iraq
History
  • Received: June 14, 2026
  • Revised: September 13, 2026
  • Accepted: September 21, 2026
  • Available Online: September 30, 2026
DOI

https://doi.org/10.65505/ETES-26-0015

Abstract

Skirted foundations are an appropriate ground improvement method for improving the performance of shallow foundations built in sandy soils. This paper reports an experimental study on the effect of the skirt length and foundation size on the performance of circular foundations under vertical loading on medium-dense dry sand. Six laboratory model tests were made, of which two were unskirted and four skirted foundations. Two (2) different diameters of circular footings, 60 mm and 90 mm, were tested with two different lengths of the footing skirts (L/D), 0.5 and 1.0. Terzaghi's criterion, in which the settlement is 10% of the footing diameter, has been used to determine the ultimate bearing capacity. The results showed that the use of skirts was significantly helpful to improve the load–settlement response, increase the foundation stiffness, and increase the ultimate bearing capacity. The ultimate load for the footing of diameter 60 mm was increased from 0.167 kN to 0.304 kN, which is about 82% increase when the footing is skirted with L/D = 1.0. The same trend applied to the 90 mm diameter footing, where the ultimate load went from 0.343 kN to 0.677 kN, which is about 97% improvement. The bearing capacity of foundations with L/D = 0.5 increased by 29% and 43% for footing diameters of 60 mm and 90 mm, respectively. The experimental results also showed that as the skirt increased in length, the settlement decreased, and the failure mechanisms were more stable and deeper due to the increased soil confinement and passive resistance along the walls of the skirts. Further, all skirts yielded higher failure loads with larger foundation diameters. The study has verified that the length of skirts and foundation size are important parameters that control the performance of circular skirted foundations on sandy soils. The application of skirts is an effective and cost-efficient way to increase bearing capacities, decrease settlement, and enhance shallow foundation stability.

Keywords

References

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