Studies On Ultimate Bearing Capacity Of Skirted Spudcan Foundations In Clay For Offshore Platforms

Ocean jack-up drilling platform is widely used in energy exploration and exploitation in China,The jack-up drilling platform adopts the spudcan foundation to undertake the support role of the seabed on the platform,so the spudcan foundation needs to provide sufficient bearing capacity.Some studies show that adding the extra skirt structure of spudcan foundation can effectively improve the bearing capacity.The research conditions on the bearing capacity of the existing skirted spudcan foundations are relatively simple,especially in the clay foundation or deep buried conditions.In order to ensure the safe production of ocean jack-up drilling platform,it is very important to carry out the ultimate bearing capacity of skirted spudcan foundations in clay.This paper considers the clay intensity,skirt length,buried depth,loads and other factors to study the ultimate bearing capacity of skirted spudcan foundations.The element calculation model for numerical research is established by using finite element analysis software ABAQUS.The simulation discusses the unidirectional limit bearing capacity and failure mode of skirted spudcan foundation under different soil properties,burial depth and skirt length conditions,to consider the influence of buried depth and skirt length on the ultimate bearing capacity of skirted spudcan foundation,to explore the change of soil flow damage mechanism.Explore the ability of skirted spudcan foundation to resist composite load,and explore the influence of skirt length on the composite bearing capacity and foundation damage envelope of skirted spudcan foundation.the following conclusions were drawn:(1)The value of the limit bearing capacity of the normal consolidated soil(Su=0.1k Pa+1.2z)and the super consolidated soil(Su=5k Pa+1.2z)is almost not different in the deep buried skirted spudcan foundation.In the case of deep burial,the bearing capacity coefficient of homogeneous soil,normal consolidated soil and super-consolidated soil is almost unchanged with the increase of the buried depth,reaching the level of the ultimate bearing capacity coefficient.(2)The spudcan foundation of four kinds of different skirt showed that the ultimate bearing capacity coefficient tended to be fixed with the increase of buried depth,and the bearing capacity coefficient of skirted spudcan foundation with skirt length increased significantly.The vertical bearing capacity coefficient of skirted spudcan foundation increases almost linearly with the skirt length ratio L / D,and the vertical bearing capacity performance is significantly improved,and the improvement degree is stable.Mounting the skirt edge also improves performance under horizontal load,but decreases as the skirt length increases.Under the bending moment load,with the increase of skirt length,the bending resistance gradually improves.(3)The unidirectional horizontal load or bending moment load have the influence of horizontal-bending moment cross coupling(H-M)effect.However,the degree of horizontal-bending moment cross coupling affects the skirt pile boot foundation by increasing the buried depth,but it will not disappear with the increase of buried depth.As the skirt length L / D increases,the skirted spudcan foundation is also affected by the cross-coupling of horizontal and bending moment.(4)When the skirted spudcan foundation is subjected to compound loading,the dimensions of the V-H,V-M and H-M loading planes of the skirt pile foundation are gradually expanded,but the expansion is not the same,the trend of expansion of the V-H(M=0)plane gradually slows down,and the trend of expansion of the V-M(H=0)plane is roughly unchanged.The tendency of the V-H(M=0)plane slightly slightly.In the loading plane of H-M(V=0),the asymmetry of the foundation broken envelope increases with the skirt length ratio L / D,and the eccentricity of the broken envelope gradually increases to the negative direction of the coordinate axis of the horizontal bearing capacity coefficient.This paper effectively expand the clay foundation skirted spudcan foundation limit bearing capacity research,It can provide some scientific basis and technical support for the research on the ultimate bearing capacity of jack-up drilling platform skirted spudcan foundation in offshore oil and gas exploitation in China.It can provide some reference for scientific research and practical engineering to reduce the occurrence of ocean jack-up drilling platform accidents.