广义单排管冻结稳态温度场解析解

Generalized analytical solution to steady-state temperature field of single-row-piped freezing

  • 摘要: 人工地层冻结工法将土体中水变成冰,形成冻土,提高土体自身的承载力,是地下工程理想的加固体与止水帷幕。在高地下水位软土地区,冻结法被广泛应用于盾构进出洞加固工程中,其常见的布管形式有直线排管和圈管两大类。人工冻土帷幕的力学性能与布管形式和温度分布密不可分,因此掌握不同布管形式的温度场分布是冻结工程成功的基础。现在较为流行的方法是将冻结看作准稳态过程,利用稳态公式近似计算温度场分布。对于单排管冻结稳态温度场的解,目前仅有简单布置条件下的解析解,尚无通用的解答形式。基于人工冻结稳态温度场假设,依托Бахолдин单排管模型建立相应稳态温度场的周期形式计算模型,引入狄拉克函数,利用格林函数法获得其解析解的周期表达形式,并外推获得广义单排管冻结稳态温度场解析解的矩阵表达形式; 选取1种特殊的布管形式,应用有限元软件进行冻结瞬态数值模拟,检验稳态温度场解析解用于预估瞬态温度场分布的准确性和适用性。结果表明,在单排管冻结前期,由于冻土尚未交圈,冻结管与土体热交换剧烈,解析解与数值计算结果之间存在一定的误差,但总体变化趋势是保持一致的。当冻土发展一段时间后,热交换趋于稳定状态,解析解与数值计算的吻合程度非常高,即该阶段内,利用解析解能较好得预估瞬态温度场分布情况。

     

    Abstract: Artificial ground freezing method (AGF), which turns the water in the soil into ice, improves soil’s bearing capacity itself.It is an ideal reinforcement and waterproof for the under-ground engineering.In the soft soil area with high underground water table, AGF is widely used in the project for tunneling machine launch or retrieval and the row pipes and the ring pipes are the common forms.The mechanical properties of the frozen soil are inseparable from the pipe form and temperature distribution, so it is important for the researchers in the freezing project to understand the temperature field distribution of different piping forms.The most popular method is to treat freezing as a quasi-steady state process and approximate the temperature field distribution using a steady-state formula.In terms of all analytical solutions of single-row-piped freezing, it is only available for the steady-state temperature field of the simple form.However, there is no solution for the generalized single-row-piped freezing.Based on the periodic model of Бахолдин arrangement and Dirac function, this paper establishes a periodic steady-state model and obtains its analytical solution by Green’s function method.Then, the steady-state temperature field of the generalized single-row-piped arrangement, as a matrix form, is derived.Finally, a special pipe form is simulated to test the accuracy and applicability of the analytical solution.The results show that since the frozen soil has not been intersected and the heat exchange is severe in the early stage, there is a certain error between the analytical solution and the numerical calculation.Nevertheless, the overall change trend is consistent.When the frozen soils develop for a period of time, the heat exchange tends to be stable and the analytical solution is very consistent with the numerical calculation, which means the analytical solution can be used to estimate the transient temperature field distribution.

     

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