Abstract: Grouting-screw pile is a new type of uplift pile which uses a construction technology innovation combining boring and secondary grouting, has been carried out in soft soil area. In order to conduct a further research on its bearing characteristics, so that the pile can be widely promoted, a three-dimensional finite element numerical simulation analysis of its uplift bearing performance and mechanism is carried out. Firstly, the numerical simulation of pile-soil interface indoor large direct shear test is done to get the pile-soil interface parameters. Secondly, the three-dimensional finite element numerical simulation analysis is done by using the pile-soil interface parameters obtained. Finally, through the numerical simulation, the uplift load-displacement curve and the distribution of axial force of screw piles for different values of S/D (ratio of screw pitch to pile diameter) are obtained; the development of plastic deformation of soil around the pile is observed. Numerical analysis shows that owning to the increase of skin friction of pile caused by the "mechanical occlusion effect", the ultimate uplift resistance bearing capacity of screw pile increases by 3~5 times than circular cross-section pile's; the bearing capacity is related to S/D, when the S/D equals optimum, the initial tangential stiffness of the load-displacement curves, the ultimate bearing capacity and the continuous arched plastic deformation zone of soil around the pile equal maximum.

Key words: pile foundations, grouting-screw pile, uplift pile, interface, numerical simulation