Study On Field Test And Numerical Simulation Of Vertical Bearing Capacity Of Spliced Screw Steel Piles

As a kind of pile with variable sections,screw steel piles have many advantages such as rapid installation,high bearing capacity,and environmental protection.In recent years,screw steel piles have been gradually applied to practical projects.However,the research on screw steel piles is still relatively lacking,and the design theory is not mature enough.In this paper,the vertical bearing performance and theoretical calculations of screw steel piles are studied by both two methods,the field pile static load test and the finite element numerical simulation.Also,the influence of design parameters,including length of screw steel piles,spacing between helices,depth of helices,and number of helices,on ultimate compressive bearing capacity of screw steel piles is studied.The research results obtained are as follows.(1)According to the actual project of screw steel piles,the production and installation technology of screw steel piles are summarized.(2)As the compressive ultimate bearing capacity of the screw pile is judged by the Q-s curve of the pile,0.1 times of the helices diameter can be taken as the vertical displacement corresponding to the ultimate bearing capacity of the screw steel piles.(3)The method of grouting of the expanding device is effective and have large grouting quantity,the concrete cylinder can be formed around the screw pile,which can significantly improve the ultimate bearing capacity of screw pile.(4)The spacing between helices is an important design parameter that affects the vertical bearing performance of screw steel piles.The compressive ultimate bearing capacity of screw steel piles increases first and then decreases with the ratio of spacing to diameter of the helices(S/D).According to the research results,it is suggested that S/D=4~5 be used as the optimal design range for the spacing between helices of screw steel piles.(5)The compressive ultimate bearing capacity of screw steel piles increases with the increase of pile length and helix depth,which also increases approximately linearly.The increase of the number of helices in screw steel piles can increase the compressive ultimate bearing capacity of screw steel piles.But ensuring that the spacing between helices is within the optimal range comes first,and then increasing the number of blades is considered.This can significantly improve the compressive ultimate bearing capacity of spiral steel piles.(6)Based on the research results,an improved theoretical formula for compressive ultimate bearing capacity calculation of screw pile is proposed and compared with the numerical calculation results to verify the applicability of the formula.