(A Comparative Study On The Working Properties Of Pile-Raft Composite Foundation And Pile-Raft Composite Structure)

Pile-raft composite foundation which can effectively control the total settlement and differential settlement and is easy to construct with good technical and economic indices has largely been applied in reinforcing soft foundation of high-speed railway.Pile-raft composite structure is beginning to be applied in deep soft foundation of high-speed railway recently as a simple structure which has demonstrated excellent performance characteristics.Pile-raft composite foundation under the embankment has been researched by many scholars,but the theory is still not mature.Pile-raft composite structure under the embankment is studied less.It is lack of comparative study of the two structural forms.The behavior of the two structrual forms under the high speed railway embankment were comparatively studied on basis of a fully investigation of the application and previous researcher’s work at home and abroad via theoretical analysis,in-situ test and numerical simulation.The main contents are as follows:(1) The rasearch status of Pile-raft composite foundation and Pile-raft composite structure was reviewed,and the different performances under rigid loads and embankment loads was pointed out.The problems need to be solved were brought out.(2) The settlement of the two structureal forms was calculated using a variety of methods introduced in the paper based on the structural characteristics at Cangzhou West Station of Beijing-Shanghai high-speed railway and Shangyu North Station of Hangzhou-Ningbo Passenger Railway.Based on comparison analysis between tested results and calculated results,the difference among various theoretical approach was discussed.(3) Based on the tested results of the Single-Point Settlement Meter in the railway subgrade of Shangyu North Station of Hangzhou-Ningbo Passenger Railway,the variation laws of the settlement of Pile-raft composite structure with the embankment height and the time were analyzed in subgrade-bridge transition sections,subgrade-culvert transition sections and subgrade sections.Settlement control effect of Pile-raft composite structure was statistically analysed.Differential settlement of raft was statistically analysed.The variation laws with season of Single-Point Settlement Meter and the ranson for which was analysed.The results of Single-Point Settlement Meter and Settlement plate were compared.(4) In the background Cangzhou station test section of the Beijing-Shanghai high-speed railway,the three-dimensional numerical simulation of the Pile-raft composite foundation with or without sand-gravel cushion is carried out.The settlement and mechanical characteristics were analyzed in detail.The influencing rule of sand-gravel cushion in Pile-raft composite foundation was studied.(5) In the background test section of Shangyu North Station of Hangzhou-Ningbo Passenger Railway,the three-dimensional numerical simulation of the Pile-raft composite structure is carried out.The settlement and mechanical characteristics were analyzed in detail.