Monitoring Deformation Of Deep Foundation Pit In Soft Soil Area And Analysing The Time-space Effect

Economy has developed rapidly in China’s east coastal area, and the rapid development of cities increases the demand of land resources.However, limited land resources have increasingly become the main limiting factors in city development. So the expansion and utilization of underground space now have become the mainstream trend in city development. Especially, the construction of subway has already become hot spot in the development of urban transportation. China’s east coastal area typically has soft soil foundation, and the condition of engineering geology is complex. So there are many difficulties and security risks in construction. Therefore, the study about the retaining structure’s deformation in deep foundation pit of soft soil area subway station has important practical significance. Based on the deep foundation pit project of Wuxi Metro Line 2 Liang Xi bridge subway station, the thesis uses site monitoring and numeric analysis to study the stability and enclosure system’s deformation law of subway station’s deep foundation pit. The main work includes:Combined with the special hydrogeological condition of soft soil area, the thesis does research about the stress in soft soil foundation pit’s excavation process and deformation theory. It mainly discusses the mechanism and regularity of deformation of deep foundation pit and its time-space effect. The thesis also analyses the main influence factors in deformation of deep foundation pit’s retaining structure. It turns out that in the process of foundation pit excavation and retaining, the vertical unloading on excavation face and the horizontal unloading on the soil retaining surface of retaining structure make the stress and deformation of retaining structure change with the change of time and space. Namely,time-space effect throughout the whole process of deep foundation pit excavation, and the time-space effect in soft soil foundation pit project is more significant. The main factors that influence deformation of foundation pit retaining structure are hydrological and engineering geological conditions, surroundings, the type of support system, the design of deep foundation project and the scale of the construction.Based on the Liang Xi bridge subway station’s surroundings and supporting scheme, the thesis makes a construction monitoring scheme of foundation pit engineering. It real-time monitors the stress and deformation of foundation bracing system and does research about the law presented by measured data. It is known from the analysis of monitoring data: Support system and supporting structure are important to control the deformation of foundation pit. The horizontal displacement of retaining wall and the settlement of surrounding ground surface are both less than the controlling values. Because of the rheological behavior of soft site, the time-space effect presented by deformation of foundation pit retaining structure is particularly significant.The thesis builds up a numerical analysis model to simulate the process of deep foundation pit excavation and uses FLAC3 D software to do numerical analysis about the stress and deformation of retaining structure in the whole process. It discusses the change rule of horizontal displacement and ground settlement in deep foundation pit retaining structure. The on-site monitoring data verifies the rationality and reliability of numerical simulation model.