浅覆土盾构隧道施工引起地表沉降规律研究

Analysis on Surface Subsidence by Shallow Buried Shield Tunneling

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9 m直径土压平衡盾构隧道为背景,对10、12、13、15 m 4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 d,浅埋隧道时间较长,约为4 d;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1.5倍开挖直径的范围;实测地层损失率和通过Peck公式反算的地层损失率都随隧道覆土厚度增大而减小。

To examine the patterns of the deformation of the ground surface caused by the EPB(earth pressure balance)shield in 9 m diameter passing through the stratum of sand and pebbles during tunneling,the surface subsidence,width of settlement trough,and ground loss ratio were analyzed under different thicknesses of covered soil 10,12,13,and 15 m sections of the Beijing New Airport Line.The results indicate that there is no obvious relationship between the width of settlement trough and the buried depth of tunnel.At similar parameters,the surface subsidence decreases with the increase of covered soil.Furthermore,when the soil cover on top of the tunnel is thick enough so 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 decreases as the buried depth deepened and the width of settlement trough is about 1.5 times of the excavation diameter on both sides of the middle line of the tunnel.