Study On Bearing Capability Of Pre-stressed Spun Concrete Knot Pile

Pre-stressed spun concrete knot pile(PSCKP) is a new type of pile developed on the basis of traditional pipe pile. Due to the annular and longitudinal convex ribs, the structure and bearing mechanism of PSCKP are different from pipe pile. Besides, mechanical connection method is used to connect PSCKP, displacing welding operation. At present, PSCKP has taken into great use in the field of civil engineering. However, the application of PSCKP is still in the stage of technology development and research as the whole. Based on static load tests, the bearing mechanism of PSCKP under the vertical load is studied by the method of theoretical analysis and numerical simulation. The main contents include as follows:(1) In the same soil condition, the comparative static load tests between PSCKP and other kinds of piles were carried out. The results show that the vertical ultimate bearing capacity of single PSCKP is increased by 20% compared with that of pipe pile and square pile; the vertical uplift ultimate bearing capacity of single PSCKP is 1.73 times more than that of pipe pile.(2) A load-displacement formula was established, and the computed results show that, in the middle-low load stage, the load transfer method based on the Hirayama hyperbolic model could ideally reflect the contact relationship between PSCKP and soil around the pile.(3) The stress and deformation characteristic of PSCKP under the uplift load were analyzed by MIDAS/GTS NX. The results show that a cylinder-shaped shearing surface is formed between PSCKP and soil around the pile in the middle-high load stage. The top of annular convex rib plays an active role in unloading, in other words, the axial force of PSCKP reduces evidently at the top of annular convex rib.(4) The numerical simulation results for piles with different cross section show that pile with longitudinal convex ribs only does not clearly enhance the bearing capability. However, annular ribs do a great job in improving bearing behavior.(5) The numerical simulation results for PSCKP with different rib distance show that the bearing capability of PSCKP decreases with the increase of rib distance. Taking production cost into consideration, it is reasonable to set the rib distance as 1m for 500-460 type PSCKP.