PENETRATION RESISTANCE OF JACK-UP SPUDCAN ON DENSE SAND OVERLYING LOOSE SAND

This paper presents experimental data associated with the penetration resistance of a conical spudcan penetrating a dense sand layer overlying loose sand. Saturated Ottawa sand was used as the seabed material. The instrumented 1-g physical model spudcan testing facility at National Chiao Tung University was used to investigate the variation of resistance profiles of a spudcan on a dense sand layer overlying a weaker stratum of loose sand. Based on the experimental data, it was found that the measured penetration resistance on the spudcan was in fairly good agreement with that estimated with the equations suggested by the Society of Naval Architects and Marine Engineers (2008). When the spudcan was extracted from the granular soil, the penetration resistance on the spudcan suddenly vanished. The upward moving spudcan was separated from soil particles below. For the spudcan penetrating a dense sand layer overlying loose sand, no peak penetration resistance and no abrupt post-peak softening was recorded, and no "punch-through" failure happened. The penetration profiles for a single dense sand layer and a single loose sand layer constituted the upper and lower bounds for the penetration curves for all different dense sand thickness conditions. At the critical void ratio, the backflow of soils induced a footprint sloping angle nearly equal to its residual internal friction angle, irrespective of its original density and shear strength. © 2019 Taiwan Geotechnical Society.