Soil failure mechanisms associated with spudcan foundations on clayBaden Clegg Award entry

In soft offshore deposit sites, the spudcan foundation used in jack-up rigs can penetrate up to 2- 3 times its diameter. The bearing behaviour of spudcans is directly related to the soil failure mechanism during penetration, hence the understanding of the soil failure mechanisms is important. In this study, a novel method has been developed in a drum centrifuge to examine the progressive soil failure mechanism during continuous spudcan penetration. This technique involves a model half-spudcan, a strong box with a transparent window and subsequent Particle Image Velocimetry (PIV) analysis to display the soil flows associated with spudcan penetration. A camera was also fixed above the spudcan to show the plan view of soil deformation. Two soil conditions were examined: (a) normally consolidated clay where strength increases linearly with depth and (b) clay with uniform or constant strength with depth. From this study, it was found that three distinctive soil failure mechanisms can be identified for the uniform clay: (i) surface failure; (ii) soil back flow; (iii) deep failure. The cavity formed during the initial penetration remained open until soil back flow occurred. There was no cavity formed when spudcan penetrated into normally consolidated clay. The lateral extent of soil deformation was 1.8 times the spudcan diameter in both uniform and normally consolidated clay.