Centrifugal model tests on mechanism of spudcan penetration of jack-up drilling platform in egg-shell layered soil

A jack-up drilling rig is a type of mobile platform which is commonly used in offshore engineering. Spudcan installation in stiff clay overlying soft clay is subjected to potential penetration through hazard. Penetration failure occurs when the applied load exceeds the maximum bearing resistance of the layered soil causing the spudcan to plunge into the underlying clay. In the South China Sea, the layered soil called “egg shell” or “sandwich layered soil” which is composed of thick soft-thin stiff-thick soft clay can be found. The methods for calculating penetration often used today are difficult to make right prediction for this layered soil in practice. To provide a better understanding of the spudcan bearing resistance in “egg shell” soil, centrifugal model tests are undertaken to investigate the development of the bearing failure mechanism and bearing resistance-depth profile. At the same time, the finite element method is also used to study the mechanism of penetration in the layered soil. The centrifuge tests show that the failure mechanism is governed mainly by the undrained shear strength ratio between the two layers. When the ratio of the undrained shear strength of soft clay to that of stiff clay is around 0.5 , the spudcan resistance-depth profile has two peak points; when the ratio is about 0.2 , the spudcan resistance-depth profile is the same as that provided by the other researchers. The FEM analysis shows that under different undrained shear strength ratios, the plastic zones around spudcan expand in different ways. When jack-up drilling rigs are preloaded in “egg shell” layered soil, different bearing failure mechanisms should be considered properly to prevent platform from penetration through failure.