浅层岩土结构分形对热力学特性的影响机制

Thermal anomaly is caused by the constant change of shallow geotechnical structure of North China plain. It is difficult to describe quantitatively the characteristics of stratified thermal storage and regional heat flux. According to the topographic features and analysis of section lithologic characteristics, this study includes 10 typical geotechnical research areas of Ziya River Watershed. (1) based on fractal theory and geostatistics principle, fractal model of shallow rock and soil in watershed which is in the frame of the fractal characteristic value and fractal characteristic interval is established and geotechnical structure is quantified; (2) combining the law of conservation of mass and energy, the thermal characteristics of fractal mean sample is tested indoor and heat flux is monitored in situ by field stratification. Thermodynamic properties of shallow rock and soil and the interaction between water and heat flux are identified according to the fractal model of rock and soil structure; (3) under the condition of strong changes of transpiration, buried depth of rock and soil and water content, the “knee effect” of thermal diffusion is distinguished, the influence mechanism of the fractal dimension of the particle size distribution of rock and soil structure on the thermodynamic characteristics is analyzed. Finally, a fractal thermodynamic characteristic library of shallow rock and soil structure in a typical basin is established. The quantitative geotechnical structure is used to indicate thermodynamic parameters. It provides scientific basis for revealing the migration and transformation process of stratified section material (water flow) energy (heat flow) and technical support for the accurate and effective design of shallow geothermal energy development in the area.

华北平原浅层岩土结构的持续变化导致热异常，分层热储特征、区域热流通量均难以定量描述。根据地形地貌和剖面岩性特征分析成果，立足于子牙河流域的10类典型岩土研究区，（1）借助分形理论、地统计学原理，构建以分形特征值、分形特征区间为经纬框架的流域浅层岩土分形模式，量化岩土结构；（2）结合质量、能量守恒定律，通过室内测试分形均值样品热特性、野外分层原位监测水热通量，利用岩土结构分形模式，识别浅层岩土热力学性质，以及水、热流相互作用；（3）在蒸腾发、岩土埋深和含水率强烈变化条件下，识别热扩散的“拐点效应”，剖析岩土结构粒径分布分形维度对热力学特征的影响机理，并最终建立典型流域浅层岩土结构分形-热力学特征库。利用量化的岩土结构来对应指示热力学参数，为揭示分层剖面物质（水流）能量（热流）迁移转化过程提供科学依据，为准确有效设计区域浅层地热能开发利用提供技术支持。

本项目选取华北平原典型流域的不同地貌单元进行野外定点采样，借助激光粒度仪测定PSD（颗粒粒径特征），基于研究区瞬态热线法实测热物性和岩土基本物性实测数据，利用分形理论，研究流域内分维空间变异特征；对土样结构分维进行统计分析，寻找显著影响因素，为揭示流域尺度的水力性质、建立合理的导热模型提供依据。分析了影响导热能力的主控因素，研究了不同岩性岩土热导率与比重、自然密度、干密度、质量含水率和孔隙度的关系，引入相关性分析、主成分分析等和多元统计学方法，判识影响岩土热导率的本质因素，研究岩土结构和导热能力的内在联系；利用偏最小二乘法将样本分为训练组和预测组，建立了不同岩性结构岩土的热导率预测模型。在研究上述机理过程中，对新发现的分形维数特征值进行补充野外室内试验研究，并补充了数据库，完善了流域浅层岩土结构分形-热力学特征数据库构建方法。因此，本研究在岩土水势和导热性能的表征方法与量化技术等方向，具有重要的应用价值和理论意义。受本项目资助发表了8篇国内外核心论文，共计培养了3名博/硕士研究生，本项目预算执行率99.67%。