Abstract: Variable cross-section thread pile is a new type of piles applied in ground improvement. The vertical bearing characteristics of variable cross-section thread pile are studied by means of laboratory model test and numerical simulation. The difference of bearing characteristics between variable-section thread piles and ordinary straight piles and plain cylindrical piles is analyzed. And the influence of thread structural parameters and foundation soil parameters on vertical bearing capacity of variable cross-section thread pile is comparatively analyzed. The results show that the thread structure of the variable cross-section thread pile and the round-shaped pile body can greatly improve the side friction. Under the same stratum condition, the material utilization ratio (ultimate load divided by pile body volume) of the variable cross-section thread pile is about 1.3 times that of the ordinary section thread pile, and is about 3 times that of ordinary cylindrical smooth pile. Among the structural parameters of the variable cross-section thread pile, the thread width, thickness, spacing and change rate of pile section are the important factors affecting the vertical bearing capacity of single pile, and should be fully considered in the engineering design.

Key words: variable cross-section thread pile, model test, numerical simulation, bearing capacity, structural parameters of screw thread