Large-scale Laboratory Test On Horizontal Load-bearing And Deformation Characteristics Of Large-diameter Pile And Bucket Combined Foundation Embedded In Soft Soil

Offshore wind power,as a new energy model that has risen rapidly in recent years,has advantages such as a large construction site and green pollution-free.Common offshore turbine foundation forms include suction bucket foundation,large diameter single pile foundation,tripod foundation,and jacket foundation.Among them,largediameter single piles(6-8m in diameter)have the characteristics of fast construction speed and good economy,and are widely used in European countries.In order to ensure that the deformation and rotation angle of the wind turbine foundation meet the control requirements under extreme weather such as storm surge,the horizontal bearing capacity of the pile foundation is set very high.In recent years,the engineering community has proposed a new type of foundation(large-diameter pile and bucket combined foundation).Among them,the bucket body is a wide and large foundation with a shallow depth of soil,which is more conducive to the horizontal resistance of the shallow seabed soil,thereby effectively improving the horizontal bearing performance of the pile-bucket foundation.Research on the deformation characteristics of pile foundations under existing horizontal loads is mostly for small diameter single piles(pile diameter is less than 4m)and mostly for small scale model tests(scale is less than 1:50),basically there is no large scale model test research report of large diameter pile-bucket foundation.At the same time,the p-y curve widely used in engineering design is proposed for smalldiameter single piles and is not directly applicable to large-diameter pile-bucket combined foundations.In this paper,a large-scale(1:40)model test of the horizontal bearing deformation characteristics of large-diameter single piles and pile-buckt combined foundations in soft seabed soil is carried out,respectively considering horizontal static forces and two-way circulation.This type of displacement loading mode measures the pile / bucket strain,the soil pressure and pore pressure around the pile,the displacement of the pile body,and the external load at the loading point.The loading point displacement-load curve of the pile-bucket combined foundation and the depth at various depths are obtained.The p-y curve and the comparison with the test results of a single pile reveal the improvement of the pile-bucket combined foundation on the overall horizontal ultimate bearing capacity of the pile foundation and the ultimate soil resistance around the shallow soil pile.The main research contents of this article are as follows:(1)Based on the prototype pile and on-site seabed soil,the geometry and material parameters of the model single pile and pile-bucket structure and the model test soil parameters were derived from the similarity theory(1:40).Then produced the model piles/bucket and the model test soil was loaded and preloaded;The physical and mechanical properties and strength parameters of the test soil were tested,and the undrained shear strength of the test soil after the precompression consolidation was measured;Subsequently,the bending stiffness of the model pile and model bucket was calibrated,and finish the installation work of pressure piles and monitoring elements such as strain,pore pressure,and LVDT displacement sensors;According to horizontal static and bidirectional cyclic loading methods,test scheme for the single pile and pilebucket was carried out.(2)The horizontal static loading test of large-diameter single pile and pile-bucket combined foundation was carried out,and the static p-y curves and horizontal ultimate soil reaction force at various depths of large-diameter single pile and pile-bucket combined foundation in soft clay were obtained respectively;Through the loaddisplacement curve at the loading point,the horizontal ultimate bearing capacity and initial stiffness of the pile-bucket foundation are evaluated relative to the single pile;The horizontal static loading of the pile-bucket foundation with different size bucket in the test,and the influence of the height and diameter of the bucket on the horizontal ultimate bearing capacity was evaluated.Through the pore pressure gauges arranged around the pile,the range of soil resistance around the pile-bucket combined foundation was analyzed.(3)Two-way cyclic loading test of large-diameter single pile and pile-bucket combined foundation was conducted to test the displacement,strain and pore pressure of single pile and pile-bucket foundation under different cycle frequencies and amplitudes,revealing the cyclic loading deformation development characteristics of large-diameter single pile and pile-bucket foundation;Analysis obtained p-y curve of pile-bucket combined foundation under cyclic loading;Comparative analysis of cyclic frequency and amplitude on super static pore pressure of soil around pile.