The working behavior of the screw-shaft pile is influenced by various factors, among which the screw pitch and the screw length are two key factors. To study the progressive developing law of bearing capacity and soil deformation around vertical compression screw-shaft pile under different conditions, a model test based on digital image correlation deformation measurement is carried out, and the reliability of the model test is preliminarily verified by the field test results. The research reveals the influence law of the screw pitch and the screw length on the ultimate bearing capacity of the screw-shaft pile, and the empirical expression of normalized screw pitch diameter ratio factor and screw length ratio factor is established with reasonable values under the test condition. The distribution law of soil displacement field around the shaft section, screw section, and pile tip is concluded into different settlement stages, and the failure mode of soil around the screw-shaft pile with different pile type parameters is also proposed. The research results provide an experimental basis for the optimization of designing parameters and the establishment of the ultimate bearing capacity calculation theory of the screw-shaft pile.

Through model tests based on digital image correlation technology and discrete element numerical simulation method (PFC), the influence of thread setting, the relative density of sand, loading conditions on the uplift bearing capacity, and deformation characteristics of the screw-shaft pile are studied. The test results are used to calibrate the micro parameters of the discrete element program. The simulation results are used to analyze the load sharing characteristics, the influence of pile type parameters on the bearing capacity and the sliding surface of the soil around the pile. The results show that: The uplift force-displacement curves of pile foundation present softening characteristics, and the 0.05D failure criterion is applicable to the determination of the ultimate bearing capacity of the uplift pile. The setting of the screw threads increases the bearing capacity of the pile by 37%, the load sharing ratio of the threaded section is close to 70%, and the shaft section is twice that of the compression condition. The uplift bearing capacity decreases with the increase of thread pitch. H/D = 1.00 is a reasonable parameter under this condition. The improvement of the relative density of sand makes the uplift bearing capacity of screw-shaft pile and straight rod pile increase by 19.4% and 26% respectively, while the influence of displacement mode of soil around the uplift pile is limited. The maximum influence range of soil around the screw-shaft pile is about 4D, while that of straight rod pile is about 2D.