Study On Behavior Of Piled Raft Foundation Of Super-tall Building Over Metro Tunnel

The piled raft foundation is used much more widely for its great adaptability advantage. Conventional design is generally unable to take into account the effect of superstructure stiffness, so the raft is usually designed too thick and a lot of constuction materials are wasted. Therefore, it is necessary and important to study thoroughly on interaction between superstructure and piled raft foundation. With the rapid development of a city, urban traffic has no longer met actual demand, and subway has been developed rapidly. In the process of subway construction, tunnel excavation will cause displacement of the surrounding soil, which leads to the additional internal forces and deformation of piled raft foundation. So it is great of guiding significance to study on the characteritics of piled raft due to tunnel excavation, and to ensure the safety and ecnomy of the engineering design. Based on the design practice of the tall building crossing metro tunnel, FEM software ABAQUS is employed to study the characteritics of piled raft foundation.Firstly, a three-dimensional, elasto-plastic finite element model is proposed by ABAQUS to analyze the interaction of shear wall structure, piled raft and soils. The effects of superstructure rigidity, foundation modulus, raft thickness, span length of metro tunnel and Z direction stress are analyzed. Furthermore, the effect of crossing method is studied and the most reasonable crossing method is proposed.The reactions of piles agree well with measured data.Secondly, a three-dimensional, elasto-plastic numerical simulation is conducted to investigate the deformation and internal forces of piled raft foundation due to the passage of a metro tunnel. The effects of the buried depth of tunnel, soil deformation modulus and the force of shield construction are analyzed.Thirdly, vibration response analyses of piled raft foundation due to nearby subway train running are studied with two-dimensional soil-structure finite element model. The effects of metro operation speed and the buried depth of tunnel are analyzed.Finally, according to the numerical results, the experiential design of piled raft is optimized.