Investigation Of The Effect Of Spudcan Penetration And Extraction On Adjacent Foundation

Jack-up platform is a kind of platform widely used in the field of Marine energy exploitation.Jack-up platforms such as drilling platforms,maintenance platforms and offshore wind power installation platforms rely on operation arms to work.Due to the limitation of the length of the working arm,the spudcan installation location is close to the adjacent foundation,which inevitably causes some adverse effects on the stability of the foundation.In this paper,the effect of the spudcan penetration and extraction on the displacement of mat and large diameter monopile is studied.and a simple method for evaluating the cyclic bearing capacity of mat when it is working at the bottom is proposed.First using the Coupled Eulerian-Lagrangian(CEL)method to simulate the spudcan penetration and extraction.The numerical calculation of spudcan insertion reaction is compared with the theoretical value of SNAME 2008 standard.The soil flow mechanism is compared with the centrifuge test of existing literature.The results show that CEL method can well simulate the spudcan penetration and extraction.Secondly,CEL is used to analyze the influence of the spudcan penetration and extraction near the mat under the normal consolidated clay.The effects of distance,undrained shear strength of clay and diameter of spudcan on the results are discussed.The results show that,when the spudcan penetrates,the mat moves upward;when the spudcan extracts,the mat moves downward.And the side near the spudcan is greatly affected.The horizontal displacement of mat is different under different distances.The deeper the depth of spudcan and the smaller the distance between the spudcan and the mat,the greater the influence of displacement and rotation angle of mat.The lower the soil strength is,the larger the horizontal displacement and the vertical displacement of mat are.When the diameter of spudcan decreases,the disturbance range of soil around pile shoe decreases and the displacement of mat decreases.The time when the displacement and rotation angle of mat are greatly affected by the penetrate and extract of spudcan includes the initial stage of the operation and after the completion of the extraction.Then,the influence of spudcan penetration and extraction near the large-diameter monopile is analyzed,under the condition of homogeneous hard clay.The results show that,the additional vertical displacement of large diameter pile foundation caused by the penetration and pull-out of pile shoe meets the requirements of the current code.However,the inclination angle of large diameter monopile within the range of 1.25 times the diameter of spudcan does not meet the specification requirements.The maximum displacement of large diameter monopile occurs at the initial stage of pulling out operation.At last,to solve the problem of the bearing capacity of mat is weakened under cyclic loading,a simple method is proposed.Select the dynamic load characteristic value through the cyclic loading sequence,and based on the parameters of soil obtained from the conventional marine geotechnical exploration,use the results of the test results of similar soil circulation load residue and cumulative deformation in the existing literature,to quantitatively analyze the effect of cyclic loading on the bearing capacity of the mat.Taking an oilfield site in Beibu Gulf of South China Sea as an example,from the perspective of bearing capacity,this method is used to verify the feasibility of the mobile multifunctional platform with large mat.It is considered that the bearing capacity of mat under cyclic loading can be checked in the oilfield site.