The Numerical Analysis Of Stability Of Retaining Wall In Deep Excavation Of The Subway Station In Soft Clay

21^st century is the century for the exploration of the underground space and also the century for the 4th upsurging development of the geotechnical engineering. The characteristics of the upsurging of the geotechnical engineering development are the improvement of urban environment and the environmental protection. In order to achieve this goal, underground exploration is an inundate tendency for the future development of the modern city. A lot of the geotechnical engineering problems will appear inevitably. Pit excavation stability is one of the focused problems for the underground excavation. Support system stability is the important part of the pit excavation stability.Stability of the support system is a complex problem with complex factors. How to justify the buckling of the support system is the chief problem. By providing holding power to the retaining wall, the displacement of the retaining wall is confined by the shoring of the trench, consequently the stability of the trench is strengthened. The magnitude of the proper holding power will be useful for the design and choice of the strut and retaining wall. The stability of the support system is influenced by many factors, including the soil condition, strut stiffness, the magnitude of the preloading, the depth of the wall interpolating into the soil .What influence does these factors have on the stability of the support system and how to identify the proper parameter in order to guarantee the stability of the excavation and to reduce the fabrication cost. The solution of these problems relies on the systematic research. A systematic research was carried out with the engineering background of the "Shi Yi Jin" subway station excavation in TianJin China.How to simulate the whole progress of excavation is the previous problem for the research of the stability of the excavation. Therefore, the simulation of the excavation must be firstly investigated. Some problems are engaged in the simulation of the excavation progress includingsimulation of the retaining wall, preloading, the interaction between the wall and the soil, the simulation of the excavation and etc. Explicit finite difference method was used to simulate the whole progress of excavation of the "Shi Yi Jin" subway station excavation.In order to investigate the stability of the pit excavation, first of all exact definition of the stability should be given out.In this thesis, the definition of stability is divided into two categories. One is called the "structure stability", another is called the "normal using stability". The first category is according to the ultimate state of the load bearing capacity and the second one is according to the ultimate state of the normal using.The stability of the excavation was directly influenced by the magnitudes of the holding power that strut provide. Regardless of the specific strut pattern, a mechanic model was abstracted. Based on the mechanic model, the stability of the excavation with different holding power was investigated. A proper scale of the holding power was obtained through analysis.Steel pile strut is a common pattern of the strut. The pit excavation with this strut pattern usually buckles due to the lack of holding power. The stability of the pit excavation with steel pile strut was investigated according to this buckling pattern. Based on Visual Basic programming language and FLC3D software, a program was developed for the research of buckling of the pit excavation. With this program, buckling of the pit can be identified automatically and the whole progress of the buckling can be simulated. With the help of this program, the stability of the pit with different layer of strut was investigated and the optimized layer of strut was obtained.The stability of the pit excavation were influenced by many factors. With the help of the numerical simulations, some chief factors were investigated.From the above mentioned research, a new point of view of the pit excavation stability was developed. The definitions of the stability given out in the passage will have some active effect on the following research.The proper layer of the strut, proper holding power and proper magnitude of preloading force given out in the thesis can provide some experience to the design and construction of the pit excavation. The program developed in the research provides a new idea to justify the buckling of the deep excavation.