【作者】 胡坤；

【导师】 周国庆；

【作者基本信息】 中国矿业大学 ， 岩土工程， 2011， 博士

【摘要】 寒区建设工程及人工冻结工程中,土体的过量冻胀造成的危害屡见不鲜。冻土冻胀的机理研究一直是冻土界研究的热点,国内外学者提出了大量的冻胀模型,然而在一些观点上尚未达成一致。水热耦合分离冰冻胀模型能够描述分凝冰反复形成及生长特性,但该模型存在假设土体为刚性孔隙、没有考虑外荷载作用、分凝冰形成准则物理意义不清、临界分离压力取经验值等问题和不足。本文在水热耦合分离冰冻胀模型的基础上,考虑外荷载、土体孔隙变形、临界分离压力对于土体冻胀过程的影响,建立了能够描述土体一维冻结过程中分凝冰演变规律的冻胀模型;通过数值计算得到了土体冻结初期的冻缩现象;通过试验和数值计算对不同外荷载作用下的土体冻胀分凝冰演变规律进行了研究。基于能量守恒定律、傅里叶定律推导了传热微分方程;以等效水压力为水分迁移驱动力,基于质量守恒定律、达西定律推导了传质微分方程。假设土颗粒、孔隙冰为刚性介质,但土骨架考虑体积变化;考虑外荷载及土体孔隙变形对土体冻结过程的影响,改进、完善了饱和颗粒土一维冻结过程中的水热耦合控制方程。考虑临界分离压力修正了分凝冰形成准则,即以冰水交界面水膜压力为土层联系破坏力,冰水交界面水膜压力克服土体外荷载及抗拉强度时形成新的分凝冰。结合文中改进的水热耦合控制方程、修正后的分凝冰形成准则发展了更为完备的冻土水热耦合分离冰冻胀模型。对冻结缘温度变化范围内的高温冻土进行径向压裂试验,获得了冻结缘温度变化(0~-2.0℃)范围内高温冻土抗拉强度的变化规律,为土体冻胀理论模型的验证与应用提供了重要的参数。基于有限体积法对控制方程、定解条件进行离散,利用Matlab进行编程计算,将土体冻胀理论模型的数值计算结果与试验结果进行对比分析,验证了模型的适用性。通过数值计算得到了土体冻结初期的冻缩现象,与试验进行对比分析,结果基本吻合。采用刚性孔隙假设的冻胀理论模型不能获得土体冻缩现象,因为其假设土体孔隙在整个冻胀过程中不发生变化,只有产生的分凝冰才计入冻胀量,故其冻胀量计算值不可能小于零。对不同外荷载作用下饱和颗粒土的一维冻结过程进行了试验研究,结果表明,土体补水量、冻胀量随外荷载的增大而减小,并对该现象产生的机理进行了解释。基于土体冻结过程中电阻场的变化特征,提出了一种土体冻深测试新方法及装置,通过该方法得到的土体冻深曲线与热敏电阻测试结果吻合,为土体冻胀试验提供了一种新的量测手段。采用可视化、图像二值化处理等手段和方法对饱和颗粒土冻结过程中分凝冰演变规律进行试验研究,得到了饱和粉质粘土、饱和黄粘土平均分凝速率随外荷载变化的拟合函数。利用本文提出的冻胀模型进行了数值计算,结果表明,分凝冰演变规律与室内试验结果一致。通过数值计算得到饱和颗粒土冻胀过程中最暖分凝冰厚度随外荷载的增大呈指数规律减小。该论文有图110幅,表21个,参考文献138篇。更多还原

【Abstract】 There are so many hazards associated with excessive frost heave in cold regions and engineerings using artificial freezing method. Study on the mechanism of frost heave in freezing soils has been put great effort on, lots of frost heave models have been proposed by researchers, however, some different opinions still exists. Separated ice model represents characteristics of segregation ice, but some shortcoming exists, such as rigid soil porosity, ignorance of overburden pressure, critical separation pressure using empirical value. Based on the separated ice model, considering overburden pressure, deformation of soil porosity and critical separation pressure, we formulated governing equations coupled heat and moisture transfer and built up frost heave model which could explain the evolving rules of segregation ice during soil freezing. Frost shrink phenomenon was obtained during the initial period of soil freezing by numerical calculation. Finally, the evolving rules of segregation ice in different overburden pressure were studied by tests and calculations.Heat transfer differential equation was deduced based on the law of Conservation of Energy and Fourier Law; setting equivalent water pressure as driving force of water migration, moisture transfer differential equation was deduced based on the law of Conservation of Mass and Darcy Law. Soil particles and ice phase were supposed as rigid medium, soil skeleton was thought as elastomer, considering the influence of overburden pressure and deformation of soil porosity, governing equations coupled heat and moisture transfer in soil freezing were formulated. Formation standard of segregating ice was improved by using moisturefilm pressure in ice-water interface as the collapsing force, which means the segregation ice would be born when the collapsing force overcome the overburden pressure and tensile strength of soil. Separated ice model coupled heat and moisture transfer was developed by combining the governing equations and improved formation standard of segregating ice.This paper carried out split tests on high-temperature frozen soils in the temperature range of frozen fringe, obtained tensile strength of high-temperature frozen soils which varied from 0 to -2.0℃, supplied important parameters for numerical calculations.This paper discretized governing equations and definite conditions using finite volume method, calculated with Matlab and conducted comparison of calculated and experimental results, which confirmed the model feasible. Frost shrink was obtained during the initial period of soil freezing by numerical calculation which agreed well with experimental results. Frost heave model using rigid porosity assumption can not obtain frost shrink by the way of numerical calculation, because it assumes that soil porosity does not change any more during the whole process of soil freezing, only segregation ice is calculated in the formation of frost heave. Therefore, calculated frost heave using rigid porosity assumption can not be less than zero.Frost heave tests were carried out using saturated granular soils, the results showed that water uptake and frost heave diminished with the increasing of overburden pressure, and the mechanism of tests phenomenon was explained. Based on resistance variation of soils in the process of soil freezing, a new device of measuring frost depth was proposed. Frost depth results using new device agreed well with the thermal couple results. The evolving rules of segregation ice were studied by using visual equipments and binarization processing of images in frost heave tests. The average segregation rate of saturated silty clay and yellow clay were acquired, and fitting functions of average segregation rate with overburden pressure were obtained.The evolution rules of segregation ice were calculated by using frost heave model proposed in this paper, the results agreed well with experimental results. The calculated results showed that segregation ice thickness decreased exponentially with the increase of overburden in the process of soil freezing.This paper has 110 Figures, 21 Tables and 138 References.更多还原