Numerical Analysis On Influence Of Tunnel Excavation To Neighboring Existing Piled Raft Foundation In Zhengzhou

With the development of subway construction, the influences that the subway tunnel brings to neighboring existing buildings or structures have become a fundamental problem. Among them, the influence of tunnel excavation on neighboring existing piled raft foundation is an important issue that has to be confronted in the subway construction. Since there have been differences in each area of engineering geological conditions and environmental conditions of existing buildings, the degree of influence is also different. In this thesis, according to the soil conditions and building environmental conditions in Zhengzhou, a model of the tunnel excavation and neighboring piled raft foundation interaction will be established, and the interaction mechanism of tunnel-pile-soil will be discussed. This thesis will mainly conduct a research about the influences that the tunnel excavation brings to neighboring existing piled raft foundation.Based on the basic principles of the displacement controlled finite element method (DCM), the calculation method of the relevant parameters of the tunnel boundary conditions in displacement controlled finite element method (DCM) will be studied in this thesis. In comparison with other methods, DCM provides a theoretical basis for subsequent analysis of influences that the tunnel excavation brings to adjacent piles. On the basis of analyzing the interaction mechanism of tunnel-pile-soil, the model of the interaction between tunnel excavation and neighboring piled raft foundation is established. Using second-development interface of ABAQUS soft, this thesis crafts the pile-soil interface Goodman element embedded computer program. Comparative study with other results of literature will be conducted and the rationality of this thesis will be proved. Finally, according to the characteristics of soil in Zhengzhou, the computation models of interaction between tunnel excavation and pile raft foundation in eastern and western zone of Zhengzhou are established, and the internal force and deformation influence rules of piled raft foundation under different soil will be found out. The main achievements of this thesis include:(1) Through Comparative analysis with other literature, we can find that:with smaller ground loss ratio (no less than3%), simulation of interaction of tunnel-pile-soil can be implemented in displacement controlled finite element method (DCM).(2) Through metrical simulation methods, the internal force and deformation influence rules of piled raft foundation in eastern and western zone of Zhengzhou are comparatively analyzed, then we can make a conclusion that the results of piles in eastern and western zone have the same variation law, but soft soil in eastern zone lead to larger changes than that of the western zone.(3) Since the front row piles are closer to the tunnel, ground loss has an obvious influence on the front row piles, and the variation of their force and deformation are more serious than other piles. Besides, the bending moment and axial force, the changing trends of all piles are generally similar.(4) Curves of ground surface settlement caused by tunnel excavation in eastern and western zone of Zhengzhou with Gaussian distribution curve are generally the same. The upper load of pile foundation has greater impact on settlement, resulting in the increase of Pile settlement in the pile side and asymmetrical settlement trough, which further result in the maximum surface settlement points moving to non-pile side. This phenomenon of eastern zone is more obvious than that of the western zone.(5) In terms of the influences that the tunnel excavation brings to neighboring piled raft in Zhengzhou, it has been proved that the changes of ground loss ration has more obvious effect on the result of calculation, but has slight influence on bending moment of piles. It can be also found that only when the ground loss ratio is kept below3%in Zhengzhou, can the safety of construction work be ensured. The variation of the horizontal distance between pile and tunnel has obvious influence on pile lateral displacement, ground surface settlement and bending moment that caused by tunnel excavation. The variation of the upper load only has influence on the ground surface and the settlement of pile foundations but hardly affect other results.