Spudcan punch-through in thin clay crust overlying soft clay

Abstract

The presence of clay crust overlying soft clay in parts of Southeast Asian Sunda Shelf may result in punch-through hazard during jack-up spudcan installation due to the potential for reduced (or softening) bearing resistance upon failure of the crust layer. In view of the above, a series of centrifuge model tests have been undertaken on circular spudcans with prototype diameter of 10 m on layered clay samples. The thicknesses of the upper crust layer adopted in the tests ranged from about 0.16 to 0.71 spudcan diameter while the strength ratio of the lower layer to the upper layer is 0.2. This paper presents experimental results obtained in terms of 1) the development of bearing resistance upon spudcan penetration in the layered clay samples, and 2) the development of soil deformation and failure mechanisms upon spudcan penetration. The shape of bearing resistance versus penetration curves changes from ductile (non-softening) to brittle (softening) profiles as the crust thickness increases. The observed soil deformations show punching-shear failure in the upper layer, followed by the formation of a rigid crust block beneath the spudcan. The test results and the practical implications of the findings are discussed in this paper. Copyright © 2008 by The International Society of Offshore and Polar Engineers.