Extraction response of skirted foundations and a spudcan on sand-over-clay deposits

This paper presents a comparison of extraction resistance between spudcan and skirted foundations in sand-over-clay deposits. A series of centrifuge model tests was undertaken on a spudcan and two skirted foundations, varying the length of the skirt relative to the foundation diameter. The thickness of the sand layer was also varied to cover a range of practical interest. It was found that the ultimate breakout forces of the spudcan and ‘sealed’ skirted foundations in the sand-over-clay deposits are lower than that of a spudcan in a single-layer clay deposit. On the sand-over-clay deposits, when the skirted foundations are sealed, the breakout forces are 60~61% higher than that of the spudcan. However, when the skirted foundations are vented, this difference becomes minimal, regardless of the skirt length and the effective sand layer thickness beneath the foundation, with the height of the sand plug left in the clay layer being similar to the thickness of the sand layer.