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在上海轨道交通9号线盾构隧道的近距离钻孔灌注桩微扰动施工中,预先将护钢套管旋压至超出隧道底部约3 m后,再用泥浆循环方法进行取土成孔。实测结果表明,由于钢套管的护壁作用,钻孔灌注桩成孔时在钢套管位置几乎不存在地层损失;随着钢套管旋入深度的增加,管内土体的堵塞程度越来越严重,当钢套管旋压至隧道轴线以下位置时发生相对较严重的土体挤压,导致隧道上浮,并发生竖椭圆收敛变形。为减小护壁套管旋压过程中对既有地铁隧道的影响,建议在钢套管旋入过程中同时取出套管内部分土体。
In the micro-disturbance construction of short-distance bored piles in the shield tunnel of Shanghai Metro Line 9, the steel casing is pre-rolled to about 3 m beyond the bottom of the tunnel and then mud-loosening to form holes. The measured results show that there is almost no formation loss in the steel casing due to the retaining wall of the steel casing. With the increase of the depth of the steel casing, the soil blockage in the casing is getting more and more Seriously, when the steel casing is rotated to a position below the axis of the tunnel, a relatively serious squeezing of the soil occurs, resulting in the floating of the tunnel and the vertical oval convergent deformation occurs. In order to reduce the influence on the existing subway tunnel during the spinning process of the wall bushings, it is suggested to remove some of the soil in the casing while the steel casing is screwed in.