液氮冻结二次加固在富水软弱地层小盾构接收中的应用与实测

Application and Measurement of Secondary Consolidation by Liquid Nitrogen Freezing to Small Shield Receiving in Water-rich and Soft-weak Strata

为研究富水软弱地层盾构工程单独使用水泥土加固难以解决涌水涌砂的问题,以秦淮—滨南220 k V线路盾构隧道"K4"井盾构接收工程为背景,对已有化学加固的盾构端头采用液氮垂直局部冻结进行二次加固封水,提出盾构接收时冻结实测应满足的条件,进行冻结实测及温度发展规律分析。实测表明:1)水化热影响下,冻结壁平均发展速度为81.9 mm/d,为正常液氮冻结速度的55%~68%,为常规盐水冻结速度的3.2倍;2)液氮冻结的冻结壁平均温度为常规盐水冻结的3倍;3)液氮冻结工期为常规盐水冻结的1/3~1/2;4)维护冻结期间液氮消耗量为积极冻结期间的1/3便可维持冻结壁温度。利用液氮快速冻结进行二次加固封堵涌水能有效保证工期,避免事故的发生。

It is difficult to solve the problem of water inrush and mud gushing during shield tunneling in water-rich and soft-weak strata when adopting cement for soil consolidation. As a result,the shield receiving engineering of QinhuaiBinnan 220 k V shield tunnel is taken for example,the liquid nitrogen vertical partial freezing technology is used to carry out secondary consolidation of the shield end soil which has been consolidated by chemical method. And then the necessary conditions that field measurement should meet are proposed during shield receiving; and the temperature development laws are analyzed after field measurement. The results show that：（1） Under the influence of hydration heat,the average speed of development of frozen wall is 81. 9 mm/d which is 55%-68% that of liquid nitrogen freezing rate and 3. 2 times that of salt-water freezing rate.（2） The average temperature of the frozen wall which is frozen by liquid nitrogen is 3 times that of frozen by salt-water.（3） The freezing period of liquid nitrogen is 1/3-1/2 that of saltwater.（4） During the period of maintain freezing,1/3 liquid nitrogen consumption of the active frozen period can maintain the frozen wall＇ s temperature. It is concluded that the water inrush can be sealed by using liquid nitrogen quick-freezing to consolidate secondly,so as to insure the construction period and avoid accidents.