文章结合南京纬三路过江通道长距离盾构掘进盾尾刷严重渗漏、涌砂冒水工程实例,给出了液氮冻结止水及盾尾刷更换方案,分析了高水压下液氮冻结止水总去及各分支回路中的温度变化规律,以及不同土层、不同深度的土体温度变化规律.结果表明:初期冻结管进出口处液氮温差大,6 d后基本稳定在35℃;卵石层降温速度最快,砾砂层次之,粉细砂层降温速度最慢,在距离冻结管600 mm范围内,卵石层、砾砂层、粉细砂层的冻土锋面平均推进速度分别为15.5 cm/d、12.5 cm/d、8.3 cm/d;因受隧道内空气对流换热影响,管片与土交界处温度高于土层内温度.液氮冻结13 d即已形成完整的冻结壁,开始进行盾尾刷更换,从开始冻结到完成更换总需时22 d.%A scheme for stopping water by freezing liquid nitrogen and replacing the tail brush is presented in light of the situation encountered at the Nanjing Weisanlu river-crossing tunnel,a long-distance shield driving tunnel characterized by serious water leakage,sand gushing and water inflow at the shield tail brush.The law of the tempera-ture change of the master outlet circuits and each branch circuit when using liquid nitrogen freezing to stop water un-der high water pressures and the temperature change law for the soil body at different depths are analyzed.The re-sults show that: the temperature difference of the liquid nitrogen is large at the inlet and outlet of the freezing pipe,and it reaches around 35℃after 6 days; the temperature drops fastest in the pebble layer,and the second fastest in the gravel sand layer,with the temperature cooling slowest in the silty fine sand layer; the average velocities at the frontal surface of the frozen soil in the pebble layer,gravel sand layer and silty fine sand layer are 15.5 cm/d,12.5 cm/d and 8.3 cm/d,respectively,within the range 600 mm away from the frozen pipe; and affected by heat and air convection in the tunnel,the temperature at the junction of the segment and soil is higher than that in the soil layer.A complete frozen wall takes shape after 13 days of liquid nitrogen freezing,and tail brush replacement takes 22 days from freezing.
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