Punch-through Risk Analysis Of Jack-up Platform Based On The Coupling Effect Of Pile Leg And Sea Floor

Jack-up platform is the most commonly used drilling platform in offshore oil and gas field development,and it plays an important role in offshore oil and gas exploitation.Due to the complex geological conditions of the seabed,punch-through accidents are prone to occur when the platform is inserted in the layered foundation with hard top and soft bottom,which seriously threatens the structural safety of the platform and non-punch-through legs.When the platform is punctured,the difference in the degree of punch-through has different effects on the structural damage of the platform.At present,more attention has been paid to the structural response of the platform during punch-through.The in-depth research on the structural damage of the platform and the non-punch-through leg of the pile-soil coupling is less involved,and its related laws are not very clear.Based on this,this paper uses nonlinear springs to simulate the coupling effect of pile-soil on the basis of studying the coupling effect of pile leg and seabed,establishes the corresponding jack-up platform punch-through model,and uses the finite element software ABAQUS to analyze the platform under punch-through conditions.The structural damage was studied.The main research contents and results are as follows:(1)Using the small deformation finite element method,the spudcan penetration model was established,and the effectiveness of the model was verified by the centrifuge test.The changing laws of the bearing capacity of different foundations are studied,and the influence of soil characteristic parameters on the bearing capacity of foundations is analyzed.The results show that the bearing capacity of the foundation increases linearly with the increase of the cohesive force;when the elastic modulus is less than 8MP,the dilatancy angle is between 0 ??10 ?,and the friction angle is greater than 20 ?,the bearing capacity of the foundation changes greatly.(2)The horizontal bearing capacity model of the pile leg is established,and the validity of the model is verified by the centrifuge test.The force characteristics of pile legs in different types of soil are analyzed,and the influence of pile-soil parameters on the horizontal bearing capacity of pile legs is studied,and the comparison is made with the API specification p-y curve.The results show that the increase of soil elastic modulus reduces the displacement of the pile from 0.45 m to 0.34m;the increase of cohesion reduces the displacement of the pile by more than 50%;the displacement of the pile is not affected by the friction angle.(3)On the basis of the study of the pile leg-seabed coupling effect,the Pile-soil coupling effect is simulated by the Connector element(non-linear spring)in the finite element software ABAQUS,which verifies the effectiveness of the nonlinear spring model and establishes the pile-Jack-up platform punch-through model of nonlinear spring.Under the punch-through conditions selected in this paper,compared with the platform punch-through model constrained by the leg fixed supports,it is found that the largest deformation position of the non-punch-through leg is the contact surface of the leg and the seabed,and the pile-soil coupling effect can be reduced.Under the condition of preloading,the maximum stress position of pile leg is consistent with the maximum deformation position at different penetration depth.