Study On The Settlement Calculation And Structure Design Of PHC Pile Composite Foundation In Deep Soft Soil Of Beijing-shanghai High-speed Railway

PHC pile composite foundation has been widely used in treatment of deep soft soil of high-speed railway, due to it has such characteristics of less settlement, high bearing capacity and short construction period, etc. However, the research on the settlement regularity, structure design, settlement calculation theory of PHC pile composite foundation used in treatment of deep soft foundations of high-speed railway has not mature. So based on the study of composite foundation settlement test in Ji’nan west station of BeiJing-ShangHai High-Speed Railway, the paper adopted on-site testing, finite element numerical analysis,composite modulus method and Boussinesq-Mindlin united method to study the settlement regularity, settlement calculation theory of PHC pile composite foundation and optimize it’s structure, main research contents and results are as follows:(1) The paper adopted on-site testing in Ji’nan West High-Speed Railway Station to analyze the measured settlement, mainly includes regularity analysis of surface settlement, lamination settlement of composite foundation;(2) Selected section A of Ji’nan West High-Speed Railway Station as the research object, the paper established three dimensional pile group model with using ANSYS finite element, analysed settlement regularity at center position of35mPHC pile and pile length change position of35m PHC pile and25m CFG pile, and optimized the structure size, such as raft thickness, gravel cushion thickness, pile length, pile diameter, pile spacing of the PHC pile-raft composite foundation.(3) The paper adopted Boussinesq-Mindlin united method as the theoretical basis, compiled additional stress program of PHC pile-raft, pile-net composite foundation to obtain the superimposed number of piles, then combined with the layer-wise summation method to calculate the settlement. Analysed the additional stress distribution regularity of PHC pile composite foundation in different design parameters, provide certain reference for the design of PHC pile composite foundation.(4) Comparative analysed the results calculated by ANSYS finite element method, Boussinesq-Mindlin united method, composite modulus method with measured results, the paper obtained that the results of Boussinesq-Mindlin united method is close to the measured, so it indicated that the Boussinesq-Mindlin united method is suitable for the solution of PHC pile composite foundation settlement.