Large surface settlement is often caused by tunnel construction in a stratum with a soft upper part and hard lower part, and this endangers any existing buildings. Based on the Antuo-Mountain Entrance/Exit Line project of Shenzhen subway line 7 underneath the North Ring Road, a numerical calculation model is set up by three-dimensional finite differential software FLAC3D under combination of numerical simulation and field monitoring to analyze the characteristics of ground surface settlement and stratum settlement during construction of the V-shaped tunnel underneath the existing road, and a comparison and demonstration is conducted by field monitoring and measurement. The results show:1) the ground settlement trough mainly presents in a Y shape;2) the superposed effect of the crown settlement trough is obvious when the interval of two tunnels is less than 2.0D, and the superposition of ground surface settlement increases greatly when the interval of two tunnels is less than 4.0D;and 3) the influential scope of overlying ground deformation decreases with an increase of the depth. The effect of advanced support on ground surface settlement is described and a comparative study of the parameters for advanced grouting is conducted so that the construction method and support measures are optimized.%在上软下硬地层中进行隧道开挖时,常引起较大的地表沉降,危及既有建(构)筑物.文章依托深圳地铁7号线安托山停车场出入线下穿深圳北环大道工程,采用数值模拟和现场监控量测相结合的方法,利用三维有限差分软件FLAC3D建立了下穿施工过程数值计算模型,分析"八"字形隧道下穿既有道路施工过程中,路面沉降特性及地层沉降规律,并通过现场多种监控量测手段加以对比验证.研究结果表明:地表沉降槽总体呈"人"字型,在隧道间距小于2.0D时,左右隧道拱顶沉降槽叠加效应明显.在隧道间距小于4.0D时,地表沉降有较大叠加;左右隧道开挖引起的上覆地层变形影响范围随深度增加而减小,减小速度随地层深度增加而增加;通过分析模拟过程中每一开挖步引起的地表沉降量,论述了超前支护措施对控制地表沉降的作用,并就超前注浆参数进行对比研究,进而优化了施工工法与支护对策.
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