Research On Top-down Method And Deformation Pattern Of The Soil-structure System

As a new technology of deep excavation construction, top-down method can effectively reduce the foundation pit to peripheral environment, lower the construction cost and shorten the construction time. In addition, the top-down method has unique advantage on the foundation pit engineering in complex urban geological environment condition. Due to the method's complexity and particularity, it has a very important significance to study the key technology in the deep excavation with the top-down method and the deformation pattern of the soil mass and supporting system.Based on the top-down construction of Deji Plaza in NanJing, this paper discusses the key technology in the deep excavation with the top-down method and adopts the 2-dimensional finite clement analog simulation method to analyze the behavior of excavation with top-down method and pattern of the supporting system. Combine with case study, this paper firstly introduces technical principle, construction technology, technological characteristics and classification of top-down method in deep excavation construction and sums up the application, the development, and the present research state of the top-down method in the foundation pit engineering at home and abroad. According to the characteristics of the second phase top-down construction in Deji Plaza, this paper discusses dynamic decline water scheme in layers of top-down condition, and expatiates method of quality control and the key technology in the deep excavation, such as earth excavation, foundation reinforcement, construction of diaphragm wall and column pile.In view of the problem of the basin-shaped mechanical excavation in top layer and the consolidation of earth body in the diaphragm wall, this paper emphatically analyzes the effect of slope soil reserved width and foundation reinforcement scheme on the lateral deformation of diaphragm wall by FDE method. The result indicates that the basin-shaped open cut in top layer can improve construction efficiency and effectively reduce the lateral deformation of diaphragm wall before construction of shear walls.This paper summaries basic theories of FDE in excavation construction, elaborates the idea of simplified 2-dimensional FDE, a numerical simulating method of supporting structure and the technique of simulation in construction process. Based on the ADINA software, this paper constructs a FDE model of the second phase top-down construction in Deji Plaza and study numerical simulation.Lastly, based on the 2-dimensional FDE simulation, this paper systematically analyze the features of land subsidence, the rule of lateral deformation of diaphragm wall, the difference subsidence between the diaphragm wall and column pile during excavation and construction and the deformity and passive pressure characteristic of shear walls.