南京地铁7号线中胜站密贴下穿运营站MJS+水平冻结施工与实测研究

Metro Jet System and Horizontal Freezing Construction at Zhongsheng Station of Nanjing Metro Line 7 Closely Crossing Underneath an Operation Station

为解决南京新建地铁7号线在承压富水砂层近贴下穿既有10号线中胜站开挖时易发生涌砂涌水现象及冻结对既有线变形的影响问题,提出一种全方位高压喷射工法(metro jet system,MJS)+水平冻结法联合加固承压富水砂性地层的施工方法。根据实际工程,确定MJS+水平冻结加固工艺、加固参数、加固范围及冻结的方案,并通过数值模拟方法预测冻结温度场的变化规律、计算开始冻结的合理时间和积极冻结时间。对冻结过程中的土体温度、冻结及开挖过程中的既有车站底板位移进行监测,并在此基础上对暗挖方案进行优化。工程实践表明:1)冻结过程中中部MJS加固体温度一直高于端部MJS加固体温度,应当加强对中部位置温度的监测;2)冻土帷幕范围应控制在MJS加固体范围内,否则土体冻结会对冻胀变形影响较大,为此提出了上部钻孔取土泄压及间歇冻结的方案,可在一定程度上减小冻胀;3)本工程冻结及开挖阶段既有车站结构变形较小,减小了对近贴既有车站结构的影响;4)优化后的暗挖方案可加快施工进度,原开挖时间约80 d,优化后开挖时间缩短至66 d。

During the construction of the Zhongsheng station of the Nanjing Metro Line 7 closely crossing underneath the Line 10,water and sand gushing occurred and the freezing construction affected the deformation of Line 10.Therefore,the metro jet system(MJS)and horizontal freezing method are jointly employed to reinforce the water-rich sandy layer.First,the reinforcement parameters and scope of the combined construction method are determined.Then,the variation patterns of the freezing temperature field,freezing start time,and active freezing time are predicted using numerical simulations.Finally,the soil temperature during the freezing process and the displacement of the existing station floor during freezing and excavation are monitored to provide guidance for optimizing the excavation scheme.The application of the proposed method shows optimal results,and the following results are obtained:(1)During the freezing process,the temperature in the middle is higher than that at the end.(2)The range of the frozen soil wall should be controlled within the MJS reinforcement soil;otherwise,the frozen soil will considerably affect the frost heave deformation.Therefore,a scheme of upper soil sampling and gap freezing could reduce frost heave to some extent.(3)The deformation during the freezing and excavation stages is minimal,thus minimizing the impact on the adjacent existing station structure.(4)The optimized scheme reduces the excavation period from 80 to 66 days.