Bearing Capacity And Deformation Mechanism Study Of Single Pile Under Torque In Double-layered Subsoil

In recent years,with the vigorous development of offshore resources in China,bridges across ocean,offshore wind turbine foundations and offshore drilling platforms and other projects continue to emerge.And because of its advantages such as high bearing capacity,small settlement and convenient construction,the pile foundation has been widely used in such projects.Due to the harsh environment in which these projects are located,their superstructures are often are often subjected to horizontal loads such as wave loads,wind loads,ship crash loads,and superstructure installations.And these horizontal eccentric loads is usually transferred to the pile foundations,which causes the pile foundation not only to be subjected to the vertical force,the horizontal force and the bending moment,but also to the torque load which also can result in the failure of the pile.Thus,based on the existing research results and supported by the National Natural Science Foundation of China(NO.51578231;NO.51378197),this study investigated the torsional bearing behavior and deformation mechanism of circular pile in double-layered subsoil by theoretical analysis and numerical simulation.The main works are as below:At first,assuming the shear modulus of both two-layered soil is a power function with depth and with the increasing of torque,partial slip occurs between the pile and soil which will always start at the surface of the subsoil,and gradually progr ess down along the pile shaft,then considering a nonlinear variation(as a power function with depth)of the limit friction resistance along the pile-soil interface,the governing differential equation for the pile shaft under torque is established.And t hen,the solutions of the torque and the torsion angle of the pile top and the pile shaft were derived.Based on these,the MATLAB calculation program was programmed to analyze the parameters and the influence of the shear modulus of the pile,pile diameter and soil parameters on the torsional response on the pile top was obtained.Secondly,based on the ABAQUS finite element software platform,a series of 3D numerical models for a torsional pile in stiff over soft clay were established.And by comparing the results from the numerical models with available achievements,the accuracy of the models was verified,then,examine the influence of the strength ratios of the upper and lower soil layers,the relative thickness of the upper soil layer,the slenderness ratio of the pile and the roughness between the pile bottom and soil on the behavior of pile under torsional load in stiff over soft clay.At last,based on the results of numerical analysis,the stress distribution in the soil around the pile which has been twisted and the torsion failure mechanism of the single pile were discussed.In addition,simplified approximating expressions for calculating the limit torsion angle at the pile top were proposed through data fitting for the design application.