Precast Screw Pile Vertical Bearing Model Test Based On Transparent Soil And Calculation Analysis

Pile foundation is the most widely used method of foundation reinforcement in my country,and there are many types of foundation piles.Threaded piles has been widely used in China for higher bearing capacity,strong adaptability,wide application range,environmental protection and significant economic benefits when compared with traditional piles.The screw pile is a new type of threaded pile(ZL201410723263.5)independently developed by this research group,with high bearing capacity of a single pile.Research on the bearing characteristics and cross-section calculation of the new type of screw pile is helpful to reveal the bearing mechanism of screw pile.In this paper,a geometric analysis of the cross section of the screw pile is carried out,and combined transparent soil model tests with numerical simulation calculation methods to explore the vertical bearing characteristics of a single screw pile and discuss the influence of the structure parameters of the pile.The main work and results of this paper as follows:(1)The geometric analysis of the screw pile cross-section is carried out,and the calculation formulas of the area,circumference,and moment of inertia of cross-section are obtained.Using the Mathematica software,the influence law of the structure parameters of the screw pile on the section geometry is discussed.The results show that the cross-sectional area and circumference of the screw pile increase with the increasing of the radius,the thickness and height of the screw thread,and decrease with the increasing of the screw pitch.And there are two main inertia moments that differ by 13%to 72% within the parameters analyzed in this paper.What’s more,the cross-section geometric characteristics of screw pile are better than traditional round piles.(2)Transparent soil that meets the test requirements is prepared.Screw model piles are made by 3D printing technology.A model test plan for single screw pile bearing capacity based on transparent soil is designed.Model tests under 9 working conditions are carried out indoor to obtain the relationship curve of settlement and load.At the same time,the speckle field images collected in the test are processed by PIV technology to analysis the displacement field of the soil around the pile.The test results show that the bearing capacity of a single screw pile is significantly higher than that of a round pile,and the displacement field of the soil around the pile is larger than that of the round pile.The soil particles on the side of the pile and the screw teeth interlock to cause the soil producing shear deformation and exerting resistance.The soil shear strength increases the pile side resistance.The increasing of the inclination of pile increases the bearing capacity.The bearing capacity is larger when the screw pitch is optimally selected.The bearing capacity increases significantly with thread height increasing,while is less affected by thread thickness increasing.(3)The bearing process of a single screw pile is simulated based on establishing an axisymmetric model by PLAXIS finite element software.The correctness of the model is verified by comparison.The axial force of the pile,the resistance of the pile,the stress of the pile-soil interface,the shear stress of the soil around the pile are obtained.The law of influence of the pile structure parameters is discussed.The results show that the side resistance of the screw pile is large,which significantly increases the ultimate bearing capacity of the single pile.The pile-soil interface stress at the lower surface of the screw thread is relatively large,so that the soil underneath has a large shear stress and shear deformation to exert the shear strength of the soil.When the inclination angle of the pile is 0.5°～1°,the material utilization rate can be improved.When the ratio of the average radius to the thread pitch is 1.3～2.0,the ultimate bearing capacity is larger because of the fully exerted mechanical occlusion.When the proportion of the thread height to the outer diameter of the pile top is increased by 13%,the ultimate bearing capacity is increased by 23%.The thickness of the thread has a smaller effect on the bearing capacity of a single pile.