Research On Calculation Method Of Vertical Prestressed Retaining Piles

Cantilever retaining piles, as a kind of effective foundation pit supporting structure is widely used in the shallow foundation pit, but the displacement on the top of the pile is difficult to control. Hole bored piles are widely used in engineering due to its speed, convenient construction, good supporting stability and other characteristics. But supporting pile as a temporary supporting structure, A large number of steel bar were buried in the ground, not only cause huge amounts of waste, also caused the pollution of underground space. Based on the above two points, and combine that the bending moment of cantilever pile is mainly distributed in the side of the soil, supporting pile with prestressed is put forwarded. The eccentric vertical prestress is applied to retaining pilesto offset or partially offset the tensile stress in the lateral load. At the same time,in order to realize the recycling of vertical prestressed reinforcement and furtherly reduce the cost, vertical prestressed u-shaped arrangement of prestressed reinforcement retaining piles new supporting technology has been developed.Although this type of structure has been put forward and applied, but the calculation theory hasn't been reported. Theoretical research is far behind the engineering practice.In this paper.through the analysis of the mechanical characteristics of cantilever retaining piles, the vertical prestressed bolting pile internal force and displacement calculation method and design method have been proposed. In a foundation pit engineering as an example, the cantilever retaining pile and vertical prestressed bolting pile have been designed respectively, and made the comparison. Through research, this paper draws the following conclusion:1. According to the mechanical characteristics of cantilever pile, this paper analyzes the cantilever pile soil interaction, put forward the idea of piecewise calculation, using the excavation depth as boundary, the above is the loading segment, and calculate it according to the cantilever beam in the statically determinate structure, the following is the built-in section, calculate it according to the elastic foundation beam. Analytic calculation formula of pile internal force and displacement have been deduced.2. By analyzing force characteristics of vertical prestressed bolting piles, there is no column behavior in vertical prestressed bolting pile, and there is not buckling instability problems too.3. By setting the eccentric prestress, it can effectively reduce the displacement of pile top, strengthen the pile stiffness and crack resistance, reduce the maximum bending moment, improve the pile body internal force distribution, save steel consumption.4. Single anchor prestressed bolting pile, the bending moment will reverse, that is to say, the moment is distributed on both sides of the pile, by setting up reasonable parameters of pile and the pre-tension size, we can still set up prestressed steel in the side of soil to withstand tensile stress. The small bending moment of non prestressed side can be withstand by setting a small amount of ordinary steel. It is appropriate to do the reinforcement bythe two section bending moment respectively, which can effectively save the vertical ordinary reinforced.5. In a foundation pit engineering as an example, the depth is 5m,the embedment depth is 9 meters, the prestressed degree is 0.6,the cantilever retaining pile and vertical prestressed bolting pile have been designed respectively. And the internal force, deformation and reinforced dosage of the two kinds of schemes are compared. Compared with cantilever pile, pile top displacement of vertical prestressed bolting pile decreased 12.22 mm, reduced 42.9%, the absolute value of maximum bending moment reduce 169.5 kN.m,39.5% reduction. Maximum shear no obvious change, the distribution of the form changes. Single pile save for 125.9 yuan, the saving rate is 16.5%.Considering recycling the save will be more obvious.It can be seen that the vertical prestressed bolting pile is an economic and efficient green supporting structure and worth promoting.