岩土的非线性冻结模型试验和相似准则

MODEL TESTS AND SIMILARITY CRITERIA FOR NONLINEAR FREEZING OF ROCK AND SOIL

  • 摘要: 由于冰的比热和导热系数与水的比热和导热系数具有显著的差异性,因此土的比热和导热系数在冻结过程中是不断变化的。依据常热参数建立起来的温度场相似准则,难以准确反映土体在冻结过程中由热参数非线性引起的温度场演变。该文基于考虑热参数非线性变化的热传导微分方程,采用相似变换法导出了冻土模型试验中温度场的相似准则,并给出了采用原土进行模型试验时原型与模型应满足的相似关系。同时,在考虑第三类边界条件对相似准则影响的基础上,导出了模型土应满足的热物性相似条件。在此基础上,分别利用ABAQUS有限元软件对线性、非线性以及考虑第三类边界条件的原型和模型温度场进行了数值模拟,并对冻结过程中特征点的温度演变过程进行了分析。计算结果表明:建立的非线性导热相似准则能够正确反映原型冻土温度场的演变过程,说明模型土热参数的计算方法是合理的。同时表明,满足第三类边界条件的土体非线性冻结相似准则具有明确的物理意义和更高的实用价值。该研究成果为冻土模型试验中模型土的配制提供了切实合理的参数计算方法,为冻土水-热-力三场耦合模型试验的设计和实施提供了理论基础和技术支持。

     

    Abstract: The specific heat and thermal conductivity of soil change constantly in a freezing process due to the significant difference in the specific heat and thermal conductivity between ice and water. The similarity criterion of the temperature field, built upon constant thermal parameters, can't accurately describe the evolution of the temperature field caused by nonlinear thermal parameters in a freezing process. Based on the heat conduction differential equation that considers the nonlinear behaviour of thermal parameters, the similarity criterion of temperature field of frozen soil model test was derived. The derivation was conducted by using the similar transformation method. The similarity relation between the prototype and the model was given when the original soil was used for model test. Meanwhile, the similarity conditions of thermophysical properties of the model soil were derived, considering the influence of the third boundary condition on the similarity criterion. On this basis, the temperature fields of the prototype and the model were simulated by ABAQUS, which considers the linearity, nonlinearity and the third boundary condition, and analyzed the temperature evolution of characteristic points in the freezing process. The results show that, the established nonlinear similarity criterion of heat conduction accurately reflects the temperature field development of the prototype frozen soil, and indicate the calculation method of thermal parameters of model soil is reasonable. Meanwhile, the nonlinear freezing similarity criterion that satisfies the third boundary condition has definite physical significance and higher practical values. This study provides a practical and meaningful calculation method for the preparation of model soil in the frozen soil model test. It also provides the theoretical basis and technical support for the design and implementation of temperature-moisture-stress coupling test in frozen soil.

     

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