Spudcan bearing capacity calculation of the offshore jack-up drilling platform during the preloading process

Abstract

To predict the penetration depth of the offshore jack-up drilling platform during the preloading process, the fluid-solid coupling theory was introduced to establish the finite element model of the soil-spudcan system in saturated clay. With this model, the spudcan bearing capacity factor was numerically calculated when spudcans penetrated into homogeneous and heterogeneous clay. The results show that, the spudcan bearing capacity factor is mainly decided by soil strength and spudcan penetration depth: for soil with lower strength heterogeneous coefficient, the spudcan bearing factor has a positive correlation with the spudcan penetration depth, while for soil with higher strength heterogeneous coefficients, the correlation is negative. When the spudcan penetration depth is about 20 m, the maximum bearing capacity factor of spudcan is 10.30 (not consider soil backflow) and 12.25 (consider soil backflow), respectively. The calculation method for spudcan bearing capacity during the preloading process was given. With this method, the penetration depth of spudcan under certain soil condition for the Bohai No. 5 platform was calculated. Because the proposed calculation method considers the influences of reaction between soil and spudcan, the nonlinear property of soil, end resistance at the bottom of spudcan, and lateral resistance of spudcan during the whole preloading process, the predicted spudcan penetration depth is more reasonable and has a difference of about 20% from the result of traditional calculation methods. Key words: offshore jack-up drilling platform, spudcan, bearing capacity, soil backflow, cavity height