Instability Analysis And Study On Prestressed Anchor And Soil Nailing Retaining Structure Of Large Deep Foundation Pit In Collapsible Loess Area

In recent years, along with the acceleration process of urbanization unceasingly and emergence of high-rise and super high-rise buildings,the importance of the foundation pit engineering protrudes increasingly, which is characterized as deep,big and complex. Foundation pit supporting forms have developed from the previous single one into a variety of combined supporting methods. Foundation pit supporting structure accidents always happen as the result of complexity of the underground structure and treatment instability of foundation pit design, excavation, rainfall and water insulation, which may delay the construction period, cause the loss of plenty of manpower, material resources and financial resources and even seriously affect the safety of surrounding buildings. Corresponding research on failure mode and failure mechanism of foundation pit need to be carried on urgently. Combined with instability analysis and research on prestressed anchor and soil nailing retaining structure of large deep foundation pit in collapsible loess area, research on the loess foundation pit engineering design and construction is made in this paper.Through summarizing the research situation and progress of loess engineering domestic and foreign, this paper analyzes supporting methods systematically, instability accidents and universal instability mechanism and mode of loess foundation pit, which turns out to conclude the important influence factors to instability of the loess foundation pith including foundation pit situation, the geological environment and the external load the foundation suffers.Based on the engineering examples and with foundation pit calculation software, the paper mainly researches on the influence of water content to stability of soil nailing wall foundation pit. Considering two different conditions in calculation-soaking and no soaking, different parameters are applied to calculation such as soil nail distance, length of soil nail, incident slope angle and slope gradient, which aims to calculate slope stability safety factor of foundation pit under different working conditions. Calculation results show that: under the condition of soaking-reasonable soil nail distance comes to 1.5m, soil nailing incident angle is 10 ? and reasonable slope angle is 74?; soaking condition-the safety factor decreases, reasonable soil nail distance of 1.2m, reasonable incidence angle is 10? and reasonable slope is 71?.Measures of waterproof engineering, drainage engineering and enclosed engineering should be taken particularly at collapsible loess foundation pit engineering in the process of excavation in time.According to the specific engineering case, the numerical analysis software FLAC 3D using the strength reduction theory of the collapsible loess site of large deep foundation pit of prestressed anchor and soil nailing support structure instability analysis, the force analysis and calculation of slope safety coefficient corresponding to the simulation of the foundation pit reinforcement soil by using FLAC 3D software to the force of each stage before and after the reinforcement of the foundation to do a comparative analysis, through the actual project case verified the relevant theoretical research, finally from the construction technology process and environment impact analysis of two aspects of the foundation pit cause partial collapse, and proposed the creation of foundation pit grouting prestressed anchor steel waist beam in the corresponding slope collapse reinforcement scheme.