粘土冻结过程中的温度场演变及在冻结法施工中的应用

There are spiral spraying pile method and grouting method for soil reinforcement. With the economic development of our country, freezing method has broad application prospects in all kinds of underground engineering. But, the application of freezing method is far from universal in underround engineering.The processing method of hot-cold is a frontier subject of foundation treatment,and has the extremely broad application prospect. Heat interchange and evolution of temperature field during freezing and thawing of soil is a complex problem of stefan which is the one with moving boundary, endogenous pyrogen, and phase transformation. The evolution of temperature field of freezing and thawing of clay and the change mechanical properties of clay, as well as therelationship of temperature of thermometric aperture and true soil are studied in this research. Similarity theory, numerical calculation and model test are used integratly to establish mathematic model of hydraulic power and thermal force. Considering ice-water phase tranformation and the effect of latent heat of freezing of soil on temperature, the regular pattern of temperature are studied during freezing. Based on chamber test, the layout manner of freezing pipes are transformed to study response of temperature field. Freezing pipes are arranged respectively in single, parallel, cross. Based on the finite element model simulation results that is generated by COMSOL Multiphysics and in which infiltration flow is considered. Points for measuring temperature are located in chamber test to monitor the temperature in typical part, and modelling by mechanism of heat transmission between soil-pipe and soil-soil are studied to improve the manner of thermometric with the temperature tube vacant or filling clay. Layout of freezing temperature are parallel and perpendicular with freezing pipes. Stell pipe and pottery clay pipe are used to temperature tube. The consequence of parameters of quantity of cold, thermal transmittance, endotherm and phase transformation are studied to establish a relationship between heat interchange and evolution of temperature field during freezing and thawing of soil and mechanical properties of frozen soil after all. Thermodynamics model of freezing method construction is extablished based on the releation obtained, and applied in design and construction of freezing method of connecting aisle of subway,and field temperature are measured by tianjin metro line 2 airport extension 1#,2# connecting aisle to proof and improve the model obtained.

冷热处理法是地基处理的前沿课题之一，具有极其广阔的应用前景。岩土冻结过程中的热交换和温度场变化是一个具有移动边界、内热源和相变的复杂Stefan问题。本课题主要研究粘土冻结时温度场的演变和土的物理力学性能变化，以及测温孔温度与土体真实温度之间的关系。采用相似理论、数值计算及模型试验相结合的研究方法，建立冻结水力、热力数学模型。考虑冰水相变及土壤凝固潜热对温度的影响，研究冻结期间温度场变化规律。基于模型槽试验，变换冻结管布置方式，研究温度场响应。模型槽中设置多个测点，测温管采用钢管和陶土管，空置或填充粘土，研究土-钢管传热与土-陶土传热的机理，以改进测温方法。研究冷量、热传导、吸热、相变等参数之间的关联性，最终建立冻结过程中热交换-温度场演变-冻土力学性能之间的关系。在此基础上建立冻结法施工的热、力学模型，并将其应用于地铁联络通道冻结法设计和施工之中，并通过现场温度测试对模型加以验证和改进。

冷热处理法是地基处理的前沿课题之一，具有极其广阔的应用前景。岩土冻结过程中的热交换和温度场变化是一个具有移动边界、内热源和相变的复杂Stefan问题。本课题主要研究了粘土随温度变化时比热和导热系数的影响因素、变化机理、变化过程、表达方式以及对温度场的影响；研究了冻结过程中温度场演变的影响因素和特点以及土的物理力学性质的变化。采用相似理论、数值计算及模型试验相结合的研究方法研究了粘土的冷冻过程。根据潜热的物理意义得到土的比热应该分段计算，即分为融土阶段、冻结阶段和冻实阶段。在融土阶段，孔隙水始终为液态；在冻结阶段，存在可以进一步冻结为冰的液态水；在冻实阶段，不再存在进一步可能冻结为冰的液态水。在此基础上，给出了涵盖潜热的冻土比热计算方法。在复合材料导热系数经验公式的基础上，建立了随温度变化的冻结阶段导热系数理论模型，给出了土在常温阶段、冻结阶段和冻实阶段的导热系数计算模型。研发出一种三维应力状态测试装置和一种三维应变测试装置并首次在土的冷冻模型试验中进行了应用研究。基于MATLAB PDE工具箱进行了土体冻结瞬态温度场模拟。通过对模型边界及热传导条件的假设,在平面均匀传热的基础上实现了将三维热源导问题转化为依据冻结管法平面建立的二维平面问题。对比分析了模型槽中各测温点的实测值与模拟值。基于模型槽试验，变换冻结管的布置方式，研究了温度场的响应。在模型槽中设置多个测点，测试了温度变化过程，并改进了测温方法。研究了冷量、热传导、吸热、相变等参数之间的关联性，最终建立了冻结过程中热交换-温度场演变-冻土力学性能之间的关系。在此基础上建立了冻结法施工的热、力学模型，将其应用于地铁联络通道冻结法设计和施工之中，并通过现场温度测试对模型进行了验证和改进。