Fundamental Investigation of Interactions of Temperature, Pore Water Pressure, and Pore Fluid Flow in Soil Media

温度变化会引起土壤的各种变化，包括饱和粘土和粘土混合物的体积变化，渗透率的变化，以及导致诱导流动的流体密度的特殊变化。本研究的目的是通过实验和计算相结合的模型来研究土壤中温度、水压力和孔隙流体流动的基本相互作用。通过这项研究产生的知识将被用于优化核废物处理设施、地热钻孔和其他能源地质结构的设计和建设。这项研究的结果以及先进的数值模型和实验室控制实验的结果，将是热-水力-机械-化学(THMC)模型在土木工程(例如地下结构、深层地热发电厂和多年冻土地区的建筑)中应用的关键。实验模型的结果也可用于预测由于化学反应和日温度变化引起的垃圾填埋场渗透性的变化，以便更好地基于随温度变化的渗透性来估计渗漏。预期的研究成果也将有助于改进现有的地下结构热源设计规范和方法。该项目的教育和外展活动将为来自代表性不足群体的K-12和大学生提供接触STEM学科和职业的机会。该项目的工作人员将为考虑在学术界和研究领域就业的研究生提供指导。这项研究也有助于提高作为EPSCoR州之一的肯塔基州的研究素养。本研究的目的是全面研究温度对土壤行为的影响。土壤导水率随温度的变化而变化。这不仅是因为流体密度和粘度的变化，温度也可能改变沙子和粘土中的土壤结构和孔隙度。在非饱和介质中，温度升高会导致土壤干燥，并使靠近热源的水分含量降低。然而，饱和砂体中温度的变化导致了流体质量密度的空间变化。这种变化导致了浮力驱动的流动，并产生了热驱动的孔隙流体流动。即使在静水条件下，砂土中的热致孔隙流体流动也促进了地下的换热，并导致了对流换热。因此，必须考虑诱导孔隙流体流动，才能准确地模拟地下的热传递。在高渗透土壤中，需要研究热流相互作用。另一方面，热流引起渗透率的变化和体积的变化，这将导致低渗透地基(如粘土)的热固结。(1)利用温控室预测不同土类(如不同孔隙比的砂土和粘土)在不同围压下的渗透率变化；(2)分析粘土中不同温度增量下的体积变化和热固结；(3)研究高渗透土壤中热诱导孔隙流体流动对土温响应的影响；(4)考虑时间和温度依赖的土体和流体特性，预测多孔介质中热和流体流动的相互作用。目前的研究结果将对多物理和多孔介质中的流动有用。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Temperature change induces a variety of changes in soils, including volumetric change in saturated clays and clay mixtures, changes in permeability, and special variation in fluid density leading to induced flow. The aim of this research is to investigate the fundamental interaction of temperature, water pressure, and pore fluid flow in soil through integrated experimental and computational models. The knowledge generated through this research will be utilized to optimize the design and construction of nuclear waste disposal facilities, geothermal boreholes, and other energy geo-structures. The outcomes of the research, and the results of advanced numerical model and laboratory controlled experiments, will be essential for applications of thermal-hydraulic-mechanical-chemical (THMC) modeling in civil engineering (e.g., underground structures, deep geothermal power plants, and construction in permafrost areas). The results of the experimental models can also be useful to predict the permeability changes of landfills due to chemical reactions and daily temperature variations to have a better estimation of leakage based on the temperature dependent permeability. The expected research findings may also help to improve the current design codes and methodologies for underground structures surrounding heat sources. The education and outreach activities of this project will provide both K-12 and college students from underrepresented groups with opportunities to be exposed to STEM disciplines and careers. The personnel on this project will provide guidance to graduate students considering careers in academia and research. This study also help to enhance the research literacy of the Commonwealth of Kentucky, one of the EPSCoR states. The goal of this research is to comprehensively study temperature effects on soil behavior. Soil hydraulic conductivity varies with temperature. This happens not only because of changes in fluid density and viscosity, temperature might alter the soil fabric and porosity in both sand and clay as well. Temperature increments in unsaturated media result in drying soil and moisture content reduction close to the heat sources. However, temperature changes in saturated sand make the spatial variation in fluid mass density. Such a variation results in buoyancy-driven flow and, creates thermally driven pore fluid flow. The thermally induced pore fluid flow in sand facilitates heat transfer in the ground and results in heat convection even under hydrostatic condition. Therefore, induced pore fluid flow must be considered to accurately model the heat transfer in the ground. The interaction of heat and fluid flows needs to be investigated in high permeable soil. On the other hand, heat flow results in permeability variation and volumetric changes which will result in thermal consolidation in low permeable ground (e.g., clay). Four main tasks are planned to accomplish the research goal: (1) Predicting permeability variation of different soil types (e.g. sand and clay with different void ratios) under different confining stresses using a temperature controlled cell; (2) Analyzing volumetric changes and thermal consolidation for different temperature increments in clays; (3) Studying the effect of thermally induced pore fluid flow on soil temperature response in high permeable soil; and (4) Predicting the interaction of heat and fluid flow in porous media while considering time and temperature dependent soil and fluid properties. The outcomes of the current study will be useful for Multiphysics and flow in porous media.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.