Analysis On Seepage Characteristics During Suction Installation For Composite Bucket Foundation With Compartments Inside

The composite bucket foundation with compartments inside is a new type of foundation for offshore wind turbine structures,of which the compartments make a contribution to improving the towing stability and the leveling precision during the installation process.During the suction installation,seepage flow can be produced which may also affects the installation process,especially for sand soil with high permeability.In this paper,take the composite bucket foundation with compartments inside as the research project,the suction installation model tests for bucket foundation and the simulation analysis are carried out,the seepage characteristics during the installation process for bucket foundations with or without compartments are studied,plus the seepage characteristics during leveling process are studied for bucket foundation with compartments inside.The main research contents and results are as following:(1)The suction installation tests in the sand soil are carried out with two bucket models,one is a bucket with diameter 30 cm,height 12 cm,bucket thickness 2mm without compartments inside,the other is of the same dimension with compartments inside and the compartment thickness is 2mm.The variations of penetration depth with time and negative pressure are presented.The test results reveal that soil plug can be emerged due to the seepage flow which may prevent the further penetration of the bucket foundation.As for bucket foundation without compartments,the direction of seepage flow is from outside the bucket to inside the bucket during the suction installation.Vertically,the seepage field inside the bucket is upward while the direction is opposite outside the bucket.For bucket foundation with compartments,the seepage can be formed from outside the bucket to side compartments and the middle compartment.Compared to the middle compartment,seepage is more prone to form in side compartments and the absolute value of soil excess pore pressure is higher than that in the middle compartment.(2)The 2D models of bucket foundation with and without compartments are built by finite element software ADINA,the waterhead distribution situation,the seepage gradient and velocity during the suction installation and leveling process are studied.The results show that the distribution regulations of total head equipotential line and pore pressure head equipotential line of bucket foundation with compartments inside are basically the same with those of bucket without compartments.Besides,the head equipotential line in the side compartment is denser than that in the middle compartment,the seepage force and gradient are higher than those in the middle one,which is to say the seepage is more likely to be formed in the side compartment.The conclusions agree well with the test results and are unchangeable with difference compartment dimensions.(3)The leveling test results for bucket foundation with compartments and the simulation analysis results by ADINA show that if the negative pressure is merely exerted in middle compartment,seepage flows from the bottom of the side compartment to middle compartment,the maximum seepage force and gradient occur in the compartment bottom.If the negative pressure is merely exerted in side compartment,seepage flows from outside the bucket to side compartment and no seepage can be formed between the middle compartment and the side compartment,the maximum seepage force and gradient occur in the bottom of the bucket skirt.