Numerical Analysis On Residual Response Of Adjacent Piles After Spudcan Extraction

Jack-up rigs are often adopted to help drilling and work-over operations on offshore jacket platforms in its proximity.For operations in soft soils,large-diameter spudcan foundations are often penetrated deep into the soil to provide required bearing capacity for the jack-up rigs.Besides,the residual soil deformation after spudcan extraction can also make the adjacent pile bearing residual loads,which would lead to permanent stressing and deformation of adjacent jacket platform piles.And the residual loads can further combines with extreme environmental loads to be a controlling loading condition of the pile in design,therefore,it is necessary to study the residual response of adjacent pile after spudcan extraction.Few studies have been conducted on the residual soil loads after spudcan extraction,and there is no mature method to analyze the residual pile response.Thus,a method to predict the lateral residual loads on the adjacent pile after spudcan extraction is proposed in this study.First,the Coupled Eulerian-Lagrangian(CEL)is adopted to obtain the lateral pile deflection after spducan extraction and in turn determine the corresponding fitting curve of the lateral pile deflection profile by the Orthogonal Least Square method.Then the lateral additional loads can be calculated by combining the beam bending theory with the p-y curves of active pile.The proposed method was adopted to predict available centrifuge model tests,the agreement between the predicted and measured results proved its feasibility.Then,utilizing the method of computing lateral residual loads,for clay,sand and stratified fields,different influencing factors were conducted to investigate the reference conditions that the lateral residual response of adjacent piles should be considered:(1)In clay,for the fixed-head pile,the effects of lateral residual response of adjacent piles are required to be included in design when the spudcan final penetration depth is larger than 1.5 times of diameter of spudcan(1.5D).If the final penetration depth is between 1.0D and 1.5D,and when the undrained shear strength at the soil surface(s_u0)is less than 6.0k Pa and the variation speed of s_uwith depth(k)is less than 1.5k Pa/m,evaluation of the lateral residual response is necessary.If the final penetration depth is less than 1.0D,there is not necessary to consider the lateral residual response.(2)In sand,the effects of lateral residual response are required to be included in design when the spudcan final penetration depth is larger than 0.75D.When spudcan final penetration depth is less then 0.75D,if the internal friction angle is larger than 30 degree,the lateral residual response of adjacent piles should be evaluated.Furthermore,the load-transfer method was further combined with the CEL technique to form a method to predict the vertical residual loads after spudcan extraction,and its validity was also verified by comparison with available centrifuge model tests.Besides,when the clearance is 0.5D,the reference conditions that vertical residual response of adjacent piles should be evaluated were investigated:(1)In sand,the vertical residual response of adjacent piles are required to be evaluated when the spudcan final penetration depth is 0.5D.(2)In clay,when the spudcan final penetration depth is 1.0D,if the s_u0is 6.0k Pa,it is necessary to elevate the vertical residual response of adjacent piles.