Title : Re-penetration of a spudcan on sand near an existing footprint

Page : PP.141-154

Author(s) : Yung-Show Fang, Cheng Liu, and Ying-Chu Shih

Keyword : sand, Model test, footprint, spudcan., Failure mechanism, re-penetration

Abstract : 

This paper presents analytical and experimental data associated with the re-penetration of a spudcan on sand near an existing footprint. The instrumented 1-g physical model spudcan testing facility was used to investigate the variation of vertical reaction force, horizontal reaction force, and reaction moment on the spudcan with increasing penetration depth. The diameter D of the conical spudcan was 200 mm, and saturated loose Ottawa sand was used as the seabed material. Based on the experimental data, the following conclusions were drawn. For the first penetration of the spudcan, the measured vertical reaction force on the spudcan was in fairly good agreement with the theoretical solution calculated with the design guideline by the Society of Naval Architects and Marine Engineers (SNAME 2008). For the re-penetration with an offset distance equal to zero at the penetration depth from 0 to 0.1D, due to the existence of the footprint depression, the spudcan was in a “stamp-on-void” condition, and all measured reactions on the spudcan were zero. However, after the bearing spudcan surface was embedded in soil at the penetration depth of 0.15D, since the footprint soil had been heavily compressed and sheared during the first penetration, the measured vertical reaction increased rapidly with increasing depth of penetration. For the re-penetration with an offset distance of 0.5D at the penetration depth of zero, the spudcan-footprint interaction was similar to the loading of a footing on or near a slope. However, with the same offset distance at the penetration depth of 0.2D, the induced soil behavior was similar to the general shear failure below a shallow foundation. The unusual reversal of horizontal reaction and reaction moment measured with increasing depth was induced by different failure mechanisms in foundation soil at different penetration stages. When the offset distance was greater than twice the spudcan diameter, the effects of the existing footprint disappeared. For the re-penetration of spudcan on sand, the critical offset distance varied between 0.25D and 0.5D. The critical offset distance was influenced by both the penetration depth and the type of seabed soil.

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