A Numerical Investigation Into the Bottom Boundary Effect for Spudcan Penetration on Sand Overlying Clay in Centrifuge Test

In the last two decades centrifuge testing of geomaterials to meet offshore design has gained momentum. In the absence of large scale testing this technique with all its versatility has been successfully used for many offshore applications encompassing spudcan foundation, anchors, caissons, piles etc. Although many real soil failure characteristics can be replicated in the centrifuge, the centrifuge strong box may constrain the testing range when large displacement of spudcan foundation needs to be tested, especially in multiple layer soils. The paper investigates the rigid bottom boundary effect of the centrifuge strong box during large penetration of spudcan foundation into sand over clay soil profiles. Large deformation finite element (LDFE) method incorporating RITSS (Remeshing and Interpolation Technique using Small Strain) approach has been adopted for numerical simulation of the problem. With fixed vertical space available, the effects of sand layer thickness, sand friction and dilation angles have been studied. The LDFE/RITSS method was validated by existing centrifuge test data. It was observed that, during spudcan penetration, the development of sand plug trapped beneath the spudcan played a crucial role in the bottom boundary effect. The boundary effect started earlier when the ratio of sand layer thickness to spudcan diameter was greater than unity.