Properties And Design Method Of Pile-Net Composition Foundation Of High-Speed Railway Embankment

Residual settlement control and construction speed improvement are two technology difficulties if high speed railway and express road are built in soft soil. There emerged Pile-net Composite foundation, which a new way to solve stability and residual settlement control, and it is used in construction with effective performance but less theoretical research.Therefore, China National Railway Ministry made The Design Parameters for Railway and Bridge on Soft Ground Project, which responsible by The Fourth Survey and Design Institute from Ministry of Railways and Tongji University,Central South University,Shouthwest Jiaotong University, China Tie'Er'Shiju Civil Engineering Group Co., Ltd and China Tiesiju Civil Engineering Group Co., Ltd worked together. With In-situ test of Kunshanhigh-speed railway trial embankment, pile-net composite foundation have been careful studied in settlement and lateral displacement and contact pressure and pile-soil stress ratio and the stress and strain of geo-net aspects. Based on the above research, numerical calculation of Pile-net composite foundation, bearing mechanism, stability calculation and settlement law were made advanced research by test. The main conclusions of this paper are as follow:(1) In-situ testIn-situ monitor program, gauges burying schemes, in suit data connection and test frequency were confirmed, which obtained a series of in suit survey information and provide reference for similar constructions in future.(2) Test resultBased on the in-situ data, settlement and deformation of Pile-net composite foundation were studied from surface and magnetic settlement, the settlement profiles across the embankment aspects. Soil consolidation of Pile-net composite foundation was studied by Excess pore pressure dissipation data. Based on soil stress and pile soil stress ratio data, bearing and load mechanism of Pile-net composite foundation were studied and embankment fill, reinforced cushion and soil interaction were researched as well.(3) Properties of Pile-Net Composition FoundationAs far as sand pile and deep mixing pile are concerned, pile modulu and plane strain hydraulic conductivity were calculated and the finite element model was build up and every parameter was confirmed. In-situ results were compared with calculated results. Sand pile stiffness used area equivalent method, and horizontal permeability of reinforced foundation must make matching calculation, and deep mixing pile stiffness used elastic modulus equivalent method. Numerical model and calculation parameters of soft soil of foundation, reinforcement, reinforcement-soil interface and pile-soil interface are confirmed, which proved to be correct. Reinforcement axial forces, interface shear stress and interface relative displacement changes in reinforced cushion of Pile-net composite foundation were researched and parameter effect was studied as well.Safety parameters in every filling stages of Pile-net composite foundation construction were studied by Strength Reduction of the finite element model. Failure mechanics of Pile-net composite foundation and every parts effect on foundation stability were researched.Pile-net composite foundation settlement was studied by the finite element model, as well as how every parameter of foundation Pile, reinforced cushion and reinforcement effect settlement, composite foundation settlement, underlying soil layer post construction settlement and post construction settlement(4) Design MethodRange and method of reinforcement tensile stiffness, reinforcement tensile stress, reinforcement layer and interface coefficient are confirmed by test data and calculation results, which are design parameters of Pile-net composite foundation. Pile length, pile modulu, pile distances and pile diameters are confirmed by correction factor settlement as well as calculation methods. Therefore, calculation methods and steps of Pile-net composite foundation are clarified.