Lateral Bearing Behavior Of Monopile-friction Wheel Hybrid Foundation In Soft-stiff Layered Soil Deposit

Recently,in China,projects of offshore wind energy have gained an increasing development with the tendency to adopt wind turbines in deeper water s to obtain wind energy more efficiently.Compared with the vertical load from the wind turbine,the lateral load caused by wind and waves plays a more decisive role,which puts forward higher requirements for the lateral bearing capacity of the foundation.In addition,due to the complex soil layer distribution of the seabed along the depth direction in the construction area,the large-diameter monopile foundation may not be the best option for the offshore wind turbine foundation.Thus,a monopile-friction wheel hybrid foundation structure is introduced in this research,which combines the bearing characteristics of traditional monopiles and shallow foundations in the same time.It can be conducted that the hybrid foundation is more suitable for the wind tur bines built in complex marine area.However,previous researches placed emphasis on the bearing behavior of the hybrid foundation in single layer soil deposits.And the exsiting design methods of marine foundations still has limitations,especially in the coupling effect of the monopile and friction wheel during the loading process.Therefore,a group of indoor experiments and numerical analyses were conducted to investigate the failure mechanisms and bearing performances of the hybrid foundation under combined loadings in two-layer soil distributions,clay-over-sand and sand-over-clay deposits,main tasks as follows :Firstly,a group of loading tests are conducted when the hybrid foundation was in the clay-over-sand and sand-over-clay deposits based on the photogrammetry technology.The distribution of soil deformation region s during the loading procedure was obtained.Then,the soil failure surface and bearing mechanism of the hybrid foundation were obtained under lateral loading in soil deposits with two different layer distributions.Then,a group of 1g model experiments were carried out for the hybrid foundation under combined loading in the soft-over-stiff and stiff-over-soft deposits based on the in-house designed loading and measurement equipment s.The effect of the following factors on the foundation's bearing capacity were investigated : wheel diameter,lateral loading height(the height from the loading position to the mudline),soil layer distribution,the pre-vertical load on lateral bearing performance and failure characteristics of the hybrid foundation.Besides,the influence s of the parameters mentioned above on the vertical rotational position and the bending moment along the pile body in the hybrid system were also discussed.Based on these results,the author obtained the dimensionless bearing envelope s of hybrid foundation under vertical-horizontal combined forces with the influences of different parameters,and the corresponding simplified calculation formula were also concluded by fitting process.Finally,the 3D numerical analysis model was built based on the ABAQUS module.After the validation of the accuracy of the simulation results,parameter analyses were carried out to investigate the influence on the hybrid foundation bearing behavior of factors including foundation geometry,environmental combined loading and seabed soil properties.The law of the influences will provide the stability evaluation basis for the popularization and application of the monopile-friction wheel hybrid foundation in practical engineering.