Abstract
The physical properties of granular materials (such as hydraulic, strength, and thermal properties) are largely dependent on their density (or porosity) and particle size distribution. In infrastructure design, the thermal properties of soils are now more important than in the past. However, our understanding of the thermal properties of mixed granular materials is still poor. In this study, the thermal conductivity of silica sands with different porosities and particle sizes was experimentally investigated, based on ASTM D5334-14. The thermal conductivity of granular materials is presented as a function of the porosity and proportion of fine particles. The thermal conductivity tends to be low when the porosity is high and the proportion of fine particles is low (and vice versa). When the fine particles are small enough to fill the pore body of the larger particles, the coordination number increases; thus, the thermal conductivity increases when the proportion of fine particles is high. Therefore, both the porosity and particle size distribution should be carefully considered when the thermal conductivity of mixed silica sand is evaluated.
Highlights
Soils and foundations are modeled as heat sources or sinks in infrastructures, such as geothermal power plants, ground source heat pumps (GSHP), U-shaped borehole heat-exchangers (UBHE), ground heat exchanger piles, and buried pipes for steam or hot water [1,2,3,4,5,6,7]
At a vertical effective stress of 12.5 kPa, all the A–B mixed specimens started from a void ratio of approximately 0.608 and presented a decreasing void ratio with increasing load ( the mixed specimens including 90% or 100% of fine particles B were less compressed than the others (Figure 3a))
For A–C mixed specimens, the specimens with 20% and 40% of fine particles C started from a low initial void ratio (e = 0.600–0.604) and showed significant decreases in the void ratio, whereas the others showed a higher initial void ratio and lower compression (Figure 3b)
Summary
Soils and foundations are modeled as heat sources or sinks in infrastructures, such as geothermal power plants, ground source heat pumps (GSHP), U-shaped borehole heat-exchangers (UBHE), ground heat exchanger piles, and buried pipes for steam or hot water [1,2,3,4,5,6,7]. The thermal properties of soils have become more important in the design of general infrastructures because of heat-related issues in urban areas (such as heat islands, which are receiving increased attention from the public). It is well known that the amount of fine particles in granular materials influences engineering properties such as stiffness, strength, and hydraulic conductivity [10,11]. The shear stiffness of granular materials increases with a larger proportion of fine contents at a constant porosity [10]. The thermal conductivity (one of the important thermal properties of silica sand) with the varying porosity and proportion of fine particles is experimentally investigated. A transient method (ASTM D5334-14) was used to evaluate the thermal properties of mixed silica sands
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