突发渗流作用下地铁冻结工程的温度场演化特性

Evolution Characteristics of Temperature Field in Subway Freezing Engineering under Sudden Seepage

冻结法施工中,已成型的均匀冻结壁在突发渗流作用下会逐步演变为类稳态的偏心冻结壁,难以满足设计要求。为了掌握类稳态阶段土体冻结特性、形成原因并提出应对策略,对于突发渗流条件下的温度场进行仿真分析,从温度、温度梯度和热通量3个方面展开系统性研究。研究结果表明:冻结壁各位置进入类稳态阶段的时间并不相同,上游进入类稳态阶段速度快于下游,界面快于主面,距离冻结区越远,进入类稳态所需时间越短。渗流发生后上下游温度梯度将呈现明显区分,下游温度梯度极值约为上游温度梯度极值的2.0~2.5倍。土体进入类稳态阶段主要原因是该区域热通量梯度基本为零,在渗流发生后,未冻土区的对流热通量和传导热通量梯度均迅速趋于稳定,因此土体快速进入类稳态阶段。为了确定类稳态阶段冻结壁形态和性能,采用多元非线性回归方法求解出了类稳态阶段的温度场和冻结锋面,解决了实际工程中突发渗流温度场求解困难的问题。

In the construction of freezing method,the formed homogeneous freezing wall will gradually evolve into an eccentric freezing wall in the steady state under the action of sudden seepage,which is difficult to meet the design requirements.In order to understand the freezing characteristics of the soil body in the steady state-like stage,the reasons for its formation,and to propose a strategy to deal with it,the temperature field under the condition of sudden seepage was simulated and analyzed,and a systematic study was carried out in terms of temperature,temperature gradient and heat flux.According to the results,there are differences in the time required to enter the steady state-like phase at different locations along the freezing wall.Specifically,upstream enters the phase more quickly than downstream,the interface enters the phase faster than the main surface,and the time required to enter the phase decreases with increasing distance from the freezing zone.After seepage occurs,the temperature gradient of upstream and downstream will show obvious distinction,and the extreme value of downstream temperature gradient is 2.0~2.5 times of the extreme value of upstream temperature gradient.The main reason for the soil to enter the steady-state-like stage is that the heat flux gradient in the region is basically zero.After seepage occurs,the convective heat flux and conductive heat flux gradient in the unfrozen zone tend to be stabilized rapidly,and thus the soil rapidly enters the steady-state-like stage.In order to determine the morphology and performance of the frozen wall in the steady state-like stage,the temperature field and freezing front in the steady state-like stage are solved by the multivariate nonlinear regression method,which solves the problem of the difficulty in solving the temperature field of the sudden seepage in the actual engineering.