Rotational Stiffness and bearing capacity variation of spudcan under undrained and partially drained condition in clay

Abstract

Jack-up platforms are widely used to explore oil and gas resources offshore. During the operation of a jack-up, the interaction between the soil and spudcan foundation would greatly affect the distribution of bending moment on the legs, the operation and the assessment of stability of the jack-up. The first step of the present study is to investigate the rotational stiffness variation under undrained and partially drained condition using centrifuge modeling technique. A relationship which is based on the fitted curve with test data and representing the rotational stiffness variation with time was presented. The results from eleven centrifuge tests under undrained conditions were plotted in the normalized yield space. It is found that the data fit well with the yield surface. Further centrifuge tests were done to investigate the effects of soil consolidation when the jack-up is operating for a few years after the initial installation of the spudcan. the results from existing bearing capacity theories were compared with the test data under undrained condition. It is found that the approach developed by Houlsby and Martin (2003) is more accurate than the other methods. In clay with strength linearly increasing with depth, the bearing capacity variation under partially drained condition is generalized as a hyperbolic function with time. With this empirical function, the yield points lying outside the yield surface due to consolidation can be mapped into the yield surface.