Research On Bearing Capacity Of Spudcan Penetration In Stiff Overlying Soft Clay

Most offshore drilling from shallow water to intermediate water depth is carried out by jack-up rigs due to their recognized flexibility,maneuverability and cost-effectiveness.Installing spudcan foundations on the seabed to provide foundation stability during jack-up drilling platform operations.These platforms are used for offshore exploration drilling,installation and maintenance of new platforms,and oil and gas production in oilfields with limited lifetimes.The spudcan foundation is a conical foundation connected to each leg of the jack-up rig.During installation and preloading,spudcan foundations penetration is one of the important concerns in the jack-up rig industry.It has a potentially catastrophic effect on the penetration of spudcan foundations of jack-up drilling platforms,because large-scale uncontrolled penetration may cause the legs of the pile to bend,making the platform inoperable and may even cause the platform to overturn.Pile shoe penetration generally occurs in layered sediments.Recently,there have been some new design methods for predicting the bearing capacity of the spudcan foundations penetrating into the sand-covered clay foundation.In this paper,the Coupled Eulerian-Lagrangian(CEL)method is used to simulate the dynamic penetration process of large-deformation spudcan foundations,and the model uncertainty study is used to modify the four types of bearing capacity formulas recommended by the ISO for soft soil overlaid on stiff soil Four design methods suitable for predicting the peak bearing capacity of spudcan foundation penetrating into soft soil and overlying soft soil are proposed after revision,which has better prediction reference results.In addition,the random inhomogeneity of the clay seabed has long been recognized,but it was only recently that the effect of spatial variability on spudcan foundations was explicitly discussed through stochastic finite element analysis,but no studies have been conducted on multiple layers of soil.In this study,large deformation finite element calculation and random field theory are combined in the Monte Carlo simulation framework.The Coupled Eulerian-Lagrangian calculation method is used to consider the strain softening effect and the strength linearly increasing with depth.The continuous penetration of soft soil foundation over stiff soil is numerically simulated.The results show that the randomness of the soil strength has a significant impact on the soil flow and destruction mechanism,which in turn affects the bearing capacity of the spudcan foundation.It is found that the lognormal probability distribution function fits the distribution of the bearing capacity coefficient well.The correlation between the failure probability and the safety factor is established to clarify the reliability level corresponding to different safety factors.This correlation may contribute to the further development of reliability design.