【摘要】 针对富水上软下硬复合地层盾构开仓作业面临的地层失稳、涌水风险高等核心难题，采用有限元数值模拟方法揭示了富水软硬复合地层液氮冻结的作用机制，并探讨了液氮流入温度、液氮流量、冻结时间对冻结效果的影响规律。研究结果表明：1）液氮冻结法可在富水花岗岩地层中快速形成有效冻结帷幕，实现3.2 m厚冻结帷幕在5 d内快速成型。2）数值模拟结果与现场监测数据吻合度较高，验证了数值计算模型的可靠性，为冻结参数优化提供了有效的技术路径。3）液氮流入温度主要影响维护冻结阶段土体的降温速率，当液氮流入温度相差10℃时，冻结15 d后周边土体温差可达5℃。4）液氮流量越高，冷冻扩散速度越快，当液氮流量相差0.10 m~3/h时，冻结15 d后周边土体温差为2～5℃。5）冻结范围随着积极冻结时间的增加而扩大，积极冻结时间维持6 d左右即可达到设计冻结半径要求。该研究成果可为富水上软下硬复合地层液氮冻结参数的选择和优化提供技术参考。更多还原

【Abstract】 In response to the core challenges faced by shield tunneling operations in rich-water composite strata soft at the top & hard at the bottom, such as geological instability and high water inflow risks, finite element numerical simulation methods were used to reveal the mechanism of liquid nitrogen freezing in rich-water soft & hard composite strata. The influence of liquid nitrogen inflow temperature, flow rate and freezing time on the freezing effect were also explored. The research results indicate that: 1) An effective freezing curtain can quickly be formed in water rich granite formations by the liquid nitrogen freezing method, achieving rapid formation of a 3.2 m thick freezing curtain within 5 days. 2) The numerical simulation results are highly consistent with the on-site monitoring data, verifying the reliability of the numerical calculation model and providing an effective technical path for optimizing freezing parameters. 3) The inflow temperature of liquid nitrogen mainly affects the cooling rate of the soil during the maintenance freezing stage. When the difference of inflow temperature of liquid nitrogen is 10 ℃, the temperature difference of the surrounding soil can reach 5 ℃ after 15 days of freezing. 4) The higher the liquid nitrogen flow rate, the faster the freezing diffusion rate. When the liquid nitrogen flow rate differs by 0.10 m~3/h, the temperature difference of the surrounding soil after 15 days of freezing is 2～5 ℃. 5) The freezing range expands with the increase of active freezing time, and that maintaining an active freezing time about 6 days can meet the design freezing radius requirements. This research result can provide technical reference for the selection and optimization of liquid nitrogen freezing parameters in the rich-water composite stratum with soft at the top & hard at the bottom.更多还原