Study On Bearing Capacity Of Rock-socketed Pile With Steel Casing Based On Large Scale Model Test

Rock-socketed pile with steel casing is widely used in wharf construction, while the research is quite poor, which result in blindness in practical application. This thesis is based on the twelfth five year national science and technology support project-study on the key technology of navigation projects in the perennial backwater areas of three Gorges Reservoir. By doing four groups large scale rock-socketed pile with steel casing model test, all the vertical, lateral and torsion bearing capacity of pile and the load bearing behavior of steel-concrete interface are studied systematically. The main contents and results are as follows:Firstly, the rock-socketed pile with steel casing in expansion project of Guo Yuan port is taken as prototype of model piles which are devided into four groups. The test schemes of these four groups piles are designed, the scale of the former two groups is 1:7, applying vertical load and transverse load on pile to get axial strain of steel casing and steel, axial force of pile, pile side friction, bending moment of pile, and load-displacement curve. The scale of the later two groups is 1:4, applying torsion load on pile to get the strain of steel casing and concrete, and the tangential displacement of pile.Secondly, under the design vertical load and transverse load, the week position of pile is at the variable section of pile, that is the end of steel casing, the load is mainly transfered by the foundation within double pile-diameter length at the top.Thirdly, under the design vertical load, the mechanical behavior of steel-concrete interface is well, without obvious damage. Under the design transverse load, the steel-concrete interface close to foundation could be destroyed easily.Fourthly, the transverse collapse of pile includes two stages, at the first stage, the variable section of pile is snapped under the impact of “variable section effect”and the extreme point of bending moment. The destroy during the second stage is mainly depend on the relative stiffness of the fractured pile to foundation, if the stiffness of pile is larger, then the foundation could be destroyed, otherwise, the second tensile crack of pile will appear at foundation surface.Fifthly, When the pile section is under torsion, the strain distribution of the whole pile is uniform. When the steel casing is under torsion and transmit force inwards, there is obvious stress concentration at the loading location. The integral forced performance of pile is well under both situation,Sixthly, welding steel inside steel casing can improve vertical, lateral and torsion stiffness of pile, and has a little influence on steel-concrete interface when the pile is under design vertical load. It also could reduce stress concentration effectively and improves force transmission when the pile is under twist load.Finally, under the couple of vertical force and transverse force, vertical load has a great impact on the transverse stiffness of pile, and the influence is decreased with the growing of vertical load.