Study On Vertical Uplift Bearing Capacity Of Pressed Spinning Pile Head In Clay

Pressed spinning pile head is a new type of pile head which can greatly improve the bearing capacity of a single pile.By connecting the rolling bearing with the prefabricated pile,the helical blade of pressed spinning pile head has a larger lift angle.By using the reaction force of soil on the blade,the blade will spin and break into the soil.Only conventional static pressure method is needed for pile-pressing,but the torsion is not required to be screwed in,which overcomes the drawback of the excessive construction torque of the ordinary precast screw pile.At present,there is still not much understanding of uplift mechanism of pressed spinning pile head,and its load transfer,failure mode and bearing characteristics are still unclear.In this paper,the vertical uplift bearing capacity of spinning pile head in clay was studied by indoor model test,finite element numerical simulation and empirical formula.The main contents and achievements are as follows:(1)Five groups of 12 different parameters of pile types were tested in clay under static load.The variation of uplift of each pile head under different vertical loads was analyzed and the failure mode of spinning pile head was found.The test results showed that:the ultimate uplift bearing capacity of the pressed spinning pile head was much higher than that of the ordinary straight-line pile head,with an average increase of 339%.Under the same load,the uplift displacement of the spinning pile head was smaller and the uplift resistance was better.Generally speaking,spinning pile heads with low lift angle,large width and large number of blades had higher ultimate uplift bearing capacity,less uplift displacement under the same stage load and better uplift resistance.There were two kinds of failure modes of spinning pile head:cylindrical shear failure and multistage rotating spiral slip failure.(2)ABAQUS was used to carry out finite element numerical simulation,and 12 pile head models corresponding to static load test were established.The animation of the displacement distribution of the spinning pile head and soil around the pile under uplift load showed the"spinning" process of the pile body.By comparing the load-displacement curves,it was found that the variation trend of the simulated and measured values was basically the same,and the ultimate uplift bearing capacity error was less than 25%,which showed the validity of the established finite element model.(3)According to the failure mode of spinning pile head,the uplift bearing capacity of spinning pile head was studied.Referring to the empirical formula for calculating the ultimate bearing capacity of uplift piles in the Technical Code for Building Pile Foundation,considering various factors affecting the bearing capacity,the empirical formula for calculating the ultimate bearing capacity of uplift piles suitable for spinning pile head was given by fitting method.