Constrction Control Technique For Deep Foundation Of Subway Station Under Silt-Seam

In the construction process of urban deep foundation pits, the environment protection requirement on nearby environment is usually very strict, so the protection on the buildings and pipelines in the vicinity of foundation pits is the key construction points of urban deep foundation pits. The author' research project is a deep foundation pit of subway station with silt seam stratum, the stratum is very complicated and there are the features of flow-plastic property, high dampness, high sensitivity level, high coefficient of compression, low strength and low permeability. Owing to these features, the impact of foundation pit construction on the vicinity is more sensitive to construction process. The improvement of design scheme and construction process with less impact on the vicinity has evolved as an important research work.In this article, the author introduces the whole-process-control construction method of the deep foundation pit of the Huangxing Street Station of the M8 Line of Shanghai Subway. According to such features of the station as theological soil and the high environment protection requirement, the different construction measures and techniques were adopted in the different construction phrases so that the deformation of the underground continuous wall and the building settlement were effectively controlled.In this research, the author takes the all-sided analysis of the project and has the following discussions on:(1) The construction measures to avoid collapsing of slot wall and necking of underground continuous wall, in addition, the leakage resisting measures of underground continuous wall.(2) The effect of strengthened pit bottom with the cement-mud mixed piles in decreasing deformation of bracing structure.(3) The selection principle of the key parameters of dewatering prelatic water: vacuum degree and time; and the impact of leakage of support structure on nearby environment.(4) The mechanism of confined water in the absence of part stratum and safety water level.(5) The construction ideas and technical details of foundation pit support and excavation based on the space-time effect principle.(6) The interior structure effect on the deformation of support structure. First of all, especially, the key construction techniques applied in thedifferent construction phrases are mainly stated in this article; Subsequently, combining with the construction result of the project, the author analyzes the design & construction effect of the project and also points the design defect in the inserted depth of underground continuous wall and the influence extent of the different construction phrases on nearby environment; Finally it can be concluded that the rational construction parameters, the whole process control and the special controls of the key points are the fundamental rules of ensuring safety of subway foundation pit construction in the condition of siltseam stratum.