浅覆土盾构隧道施工引起地表沉降规律研究

为研究浅埋大直径土压平衡盾构施工穿越砂卵石地层造成的地表沉降规律,以北京新机场线9m直径土压平衡盾构隧道为背景,对10m、12m、13m、15m四种覆土厚度下的地表最大沉降、沉降槽宽度、地层损失率进行了对比分析,并用Peck公式进行拟合。分析结果表明：相同施工参数下,隧道上方地表最大沉降和地层损失率随覆土厚度增加而减小且成拱覆土厚度附近存在变化速率的突然改变;深埋隧道测点沉降稳定时间较短,约为2天,浅埋隧道时间较长,约为4天;实测沉降槽宽度及沉降槽拟合曲线的宽度系数与隧道覆土厚度相关性不明显,实测沉降槽宽度约为隧道中线两侧1.5D范围(D为开挖直径);实测地层损失率与通过Peck公式反算的地层损失率都随隧道覆土厚度增大而减小。

Analysis on surface subsidenceof shallow buried shield tunneling construction

In order to examine the patterns of the deformation of the earth"s surface caused by the EPB shield with 9m diameter passing through the stratum of sand and pebbles during the construction of tunnels, this thesis analyzed the surface subsidence, width of settlement trough and ground loss ratio from the project of the large-diameter EPB shield passing through different thickness of the covered soil of 10 meters, 12 meters, 13 meters and 15 meters sections of the Beijing New Airport Line. The results of the analysis indicated that there is no obvious relation between the width of settlement trough and the buried depth of tunnel and when parameters of constructionaresimilar, the surface subsidence is decrease with increasing of covered soil. Furthermore, when the soil covered on the tunnel is so thick that a "natural arch" can be formed, the surface settlement is significantly smaller than that of the shallow tunnel. In addition, the formation loss rate will decrease as the buried depth deepens and the width of settlement trough is about 1.5D on both sides of the middle line of the tunnel.