Study On Effect Of Bearing Characteristic Of Concrete Filled Core Pipe Pile Supporting Structure For Soil Excavation

Precast concrete pipe pile has been gradually used in foundation pit support engineering,because of the advantages of stable quality,low cost,fast construction speed,high pile body strength,guaranteed production and supply.This kind of support structure has succeeded in some areas.The effective section area of precast concrete pipe pile is smaller compared with the cast-in-place pile.The shear bearing capacity is low,and the whole shear failure is easy to occur.In order to solve the problem of low shear capacity of pipe pile,reinforcement the pipe pile can be reinforced by concrete filled core.And the bearing performance of filled core concrete pipe pile under the condition of soil excavation is discussed.Base on indoor model experiments,the working characteristics of hollow pipe pile and core pile under the condition of soil excavation have been compared and analyzed,and the influences of concrete core on the performance of the supporting pipe pile have been discussed.It is concluded that concrete filled core of the supporting pipe pile can effectively reduce the displacement of the pile,but has less effect on the horizontal displacement with different filled core strength.On the basis of the experiment,by FLAC3 D numerical simulation software the performances of the concrete filled core pipe pile supporting structure have been simulated and analyzed from the aspects of core strength,inner diameter,the surcharge loading and the excavation method.The results showed that:(1)The filled core can effectively reduce the horizontal displacement of pipe pile,but the core strength has less effect on the displacement.(2)The bending moment of pipe pile with different filled core strengths is slightly different when the ratio of inner diameter to outer diameter is less than 1/2,The bending moment of high strength filled core pile is smaller than the low strength filled core pile when the ratio of diameter to outer diameter is greater than 1/2.(3)when the the surcharge loading is large,the horizontal displacement at the top of the filled core pile can be reduced about 40%,and the maximum bending moment can be reduced about 30% compared with the hollow core pipepile.(4)The horizontal displacement and the bending moment of the pile can be maximum controlled by filled core and then excavating soil in a hierarchical manner.Finally,analyzed the behavior of pile on construction and foundation pit excavation process,based on the Mohr-Coulomb yield criterion,combined with Vesic cavity expansion theory,considered the compacting effect and soil arching effect,the design technique for supporting structure of cantilever concrete filled core pipe piles was established.A numeral example is proposed to prove the reliability of the theory formula which can provided basis for the design of the concrete filled core pipe pile in supporting structure.