颗粒岩土介质热导率预测关联式及其演化机制

Predicting correlation and evolution mechanisms of the effective thermal conductivity of granular geomaterials

以多相-多孔颗粒岩土介质热导率为研究对象,首先聚焦岩土颗粒几何形状特征构建细观颗粒/孔隙尺度改进型固液气三相圆柱单元结构;其次采用集总参数热电模拟法建立单元结构热导率与固液气组分热导率和孔隙率、饱和度等结构参数间的关联;进一步以饱和度参数为纽带,通过土水特征曲线类比提出统一性土-水-导热特征曲线及其演化机制概念模型。研究结果表明:(1)基于多尺度研究均质化思想建立的颗粒岩土介质热导率预测关联式模型无经验常数,各参数均有明确的物理意义,且提高了与实验测试结果的吻合度(与砂土实验测试结果的差异性比值由1.58降低至1.27,通过线性修正可进一步缩小误差至3%~16%);(2)颗粒岩土介质孔隙水分布形式与物理作用机制影响热导率的变化,不同类型(细粒含量、胶结程度)岩土介质热导率随饱和度变化曲线可以认为是由特定S型函数曲线沿低/高饱和度水平移动的演化过程,该演化机制可以解释岩土介质热导率随饱和度增加呈现出的"凹"与"凸"形增长关系,是可以统一表征不同岩土介质热导率预测模型的有效工具。

To study the effective thermal conductivity(ETC)of composite-porous granular geomaterials,an improved mesoscopic cylindrical unit cell containing three phases of solid,liquid and gas,was established based on particle geometric characteristics.The relationship between ETC of the unit cell and the thermal conductivity of each component as well as structure parameters such as porosity and degree of saturation was then obtained by using thermal-electrical analogy lumped parameter method.Taking the saturation degree as a linkage,an unified evolution conceptual model of soil-water-thermal conductivity characteristic curve(SWTCC)was further proposed via analogy analysis on soil-water characteristic curve(SWCC).The results demonstrate that the developed predicting model of ETC based on multi-scale homogenization theory not only has clear physical meaning without any empirical constant but also appears significant improvement in the coincidence degree with sandy soil experimental test results.The average ratio of the experimental value to the theoretical value decreases from 1.58 to 1.27 and can be further controlled within 1.03-1.16 through linear correction.It is also illustrated that ETC is affected by the distribution pattern and physical mechanism of pore water in geomaterials,and the shift evolution of proposed conceptual model of SWTCC can effectively explain the ETC increases in a concave and convex trend(sigmoid function)with increasing the saturation for geomaterimals with different fines contents or cementation degrees,indicating that this conceptual model is a valid tool to unify most of ETC prediction models for different geomaterials.