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以北京地铁四号线西四站为背景,选取三种开挖方案,运用FLAC3D软件对施工过程进行三维动态模拟,并在被穿越结构、地表及洞中设立监测点,计算得出各方案下土体的变形规律,并据此进行了方案优选。研究结果表明:(1)开挖顺序对地表整体平均沉降量影响不大,无论采用采用何种开挖顺序,地表最大沉降量均发生在车站中线开挖终了端;(2)三种方案对控制局部区域变形各有优势,具有“对同一项目指标,先开挖区域变形值小,后开挖区域变形值大”的规律,该规律适用于地表沉降、结构拱顶沉降、拱底隆起等指标上的评估;(3)对于中洞跨度较大的车站开挖,左(右)洞开挖对右(左)洞上方地表沉降影响不大,为了评估这种影响本文提出了“沉降贡献比值”的概念。根据对比分析,开挖方案C最优,数值模拟结果跟实测结果吻合较好。
Taking the Xisi Subway Station of Beijing Metro Line 4 as the background, three kinds of excavation schemes were selected. Three-dimensional dynamic simulation of the construction process was conducted by using FLAC3D software. Monitoring points were set up across the structure, Soil deformation law, and accordingly the program optimization. The results show that: (1) The sequence of excavation has little effect on the average total surface subsidence of the earth’s surface. No matter what kind of excavation sequence is adopted, the maximum settlement of the ground surface occurs at the end of midline excavation of the station. (2) The control of the deformation in the local area has its own advantages. It has the rule that “for the same project index, the deformation value of the first excavation area is small and the deformation value is large after the excavation area ”. This law is applicable to the settlement of the ground surface, (Left) hole excavation has little effect on the ground settlement above the right (left) hole, in order to evaluate this effect, this paper proposes a “ Settlement contribution ratio ”concept. According to the comparative analysis, the optimum excavation scheme C, the numerical simulation results agree well with the measured results.