基于Takashi实用方程的人工冻结三维冻胀预报模型研究与开发

It has been a major technical challenge to carry out construction of underground structures in water-rich and soft stratum in engineering domain. Artificial ground freezing is an effective method to solve the problems. However, frost heave is one of the objective disadvantages of the artificial ground freezing method. This disadvantage is especially outstanding in the constructions of subway and municipal geotechnical projects which have stringent requirements on the control of frost heave. At present people lack the knowledge of the frost heave mechanism and accurate prediction method for frost heave. It is becoming the major bottleneck which seriously restricts the extensive implementations of the artificial ground freezing technology. In this proposed project artificial ground freezing will be compared with natural freezing and the difference will be analyzed. Based on practical Takashi equation, an anisotropic parameter will be introduced, and then, a three dimensional frost-heave model for artificial ground freezing application will be established. Furthermore, the model is to be verified by laboratory frost heave tests. Based on systematical derivation of the finite element formulas, and combining the secondary development of ABAQUS to acquire the numerical solution for this macroscopic frost heave model, the prediction accuracy of the developed model can be accurately verified through comparing the in-situ testing data with the numerical calculation results. The research will significantly advance the effective combination of the frost heave modeling and the engineering practice of artificial ground freezing. The research results will have theoretical significance and application value in enhancing the prediction of frost heave in order to extend the implementation of artificial ground freezing technology.

在富水软弱地层中进行地下结构施工是人类工程领域面临的重大技术难题。人工冻结技术是解决该问题的有效途径。然而，冻胀是人工冻结法的客观弊端。这一弊端在对冻胀量控制要求严格的地铁和市政岩土工程施工中尤其突出。对人工冻结冻胀机理认识不足，缺少针对冻胀量的准确预测方法成为制约该项技术推广应用的主要瓶颈。本项目基于对人工冻结与天然冻结差异性的比较分析，以Takashi一维冻胀方程为理论基础，通过引入各向异性参数，构建面向人工冻结工程应用的三维冻胀模型。进而，通过室内冻胀试验对该模型进行验证。在系统推导出该模型的有限元计算公式的基础上，结合ABAQUS软件的二次开发以实现对这一冻胀模型的数值求解，将人工冻结冻胀原位观测数据与基于该冻胀模型的冻胀数值计算结果加以对比，进一步验证该预测模型的预测。该项目研究对于促进冻胀模型研究和人工冻结工程实践的有机结合，提升人工冻结工程冻胀预测水平具有理论意义和应用价值。

根据以往冻胀预测模型未考虑地铁隧道人工冻结法施工属于三维冻胀的实际请况，提出了以Takashi一维冻胀方程为理论基础，引入各向异性参数，通过水、热、力耦合分析进行人工冻结冻胀预测的这一研究思路和理念。首先针对冻结过程中的热分析这一组成部分，推导了基本的控制方程，并将有限单元法应用于热分析中，采用等效热容法估算由冰水相变引起的相变潜热。并通过一些简单的例子验证了这一计算方法的可靠性。进而从基本控制方程出发，描述了冻结过程中的力学分析。同时这一力学分析包含了由Takashi方程的冻胀率参数。这一力学分析的的主要目的是：计算冻结方向的约束应力；评估由冻胀带来的对应力的影响，并通过试验验证了这一模型的模拟准确性。讨论了由冻结过程中的水流对热状况的影响和非饱和冻胀，根据这一目的，推导了考虑非饱和和饱和状况下的水流控制方程。引入了与土体比热容和压力相关的含水量经验方程，此外，假定未冻土的渗透系数和水压相关，由于冻土的渗透系数很小，计算时其值取零代替。基于这一水力分析，首先用简单实例验证了这一计算的正确性，然后通过实例说明了非饱和土试样的冻胀和由水流所带来的热影响。. 基于以上水、热、力方面的研究工作和成果，以Takashi方程为预测模型的核心，以此来预测冻胀率，并通过水、热、力耦合分析，初步建立了人工冻结三维冻胀预测模型。并通过室内模型试验验证了该预测模型的精度和可靠性，实现了地层人工冻结冻胀预测水平的提升。

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