一维压缩条件下砂-黏土混合物热导率演化规律 English Version
Thermal conductivity evolution of sand-clay mixtures under one-dimensional compression
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摘要: 为揭示应力条件下天然砂-黏土混合物热导率的演化规律，通过一维压缩试验、干密度和热导率测试，研究混合物干密度ρd、热导率k随应力水平和黏土掺量f的变化规律、孔隙液对混合物堆积特性和传热效率的影响，基于二元介质堆积理论，构建考虑应力状态和黏土掺量的混合物热导率计算模型，同时探讨了混合物结构演化特征和微观传热机理。结果表明：砂-黏土混合物干密度ρd随黏土掺量f增加呈“先增大、后减小”趋势，f在30%~40%范围时，ρd值最大；增大竖向应力有利于提升混合物压实特性，孔隙液对ρd值影响甚微；热导率k变化与ρd相近，但孔隙液既显著降低颗粒间热阻，又提高k对f和应力水平变化的敏感性，最大热导率值发生在f=40%附近；混合物临界掺量f*、最小孔隙比emin与应力状态、孔隙液和颗粒形貌等密切相关；提出的混合物热导率计算模型综合考虑了应力水平和组分含量的影响，具有良好的适用性；颗粒变形与破碎以及空间结构演变是进一步揭示多元颗粒混合物传热机制的重要内容。Abstract: The aim of this study was to reveal the evolution law of natural sand-clay mixtures under varied stress conditions. A serial of one-dimensional compression tests, dry density, and thermal conductivity measurements were conducted on both dry and saturated samples to investigate the variations of dry density ρd as well as thermal conductivity k with increasing stress level and clay content f, and the influences of pore fluid on packing behaviors and heat flow efficiency of the mixtures. Based on the binary packing theory, a new thermal conductivity model of sand-clay mixtures considering effects of stress state and clay content was developed and verified. In addition, the microstructure characteristics and the thermal conduction mechanisms of binary granular mixtures were discussed. The results indicated that dry density ρd of sand-clay mixtures exhibits a trend of ‘increasing first and then decreasing’ with an increase in clay content f, where maximum ρd value is detected as the f is in the range of 30% to 40%. Increasing vertical stress is beneficial for improving the compaction behavior of the mixtures, and the presence of pore fluid imposes a negligible effect on ρd. Thermal conductivity k presents a similar evolution with that of ρd, while pore fluid not only significantly reduce the thermal resistance among soil particles, but also increases the sensitivity of thermal conductivity to both clay content f and stress level. The maximum k value is found around f of 40%. The critical clay content f* and the minimum void ratio emin are closely related to the state of stress, pore fluid, and particle morphology. The proposed calculation model of thermal conductivity for the sand-clay mixtures comprehensively incorporates the hybrid effects of state of stress and fine content, which is also consistent with the binary packing theory and has good applicability. Particle deformation and breakage, and spatial structural evolution of the granular matter mixtures are recommended to further explore the thermal conduction mechanism.
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Keywords:
- thermal conduction /
- packing characteristic /
- granular soil /
- vertical stress /
- calculation model
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