Practical estimation of the thermal conductivity of granular soils considering grading and relative density using three physical parameters

Abstract

The thermal conductivity of granular soils is widely used for analyzing the thermal stability in geo-structure. Particle size distribution is a crucial feature in characterizing the inter-granular structure of granular materials, and the mechanism governing the grading effect on thermal properties is not fully understood. Therefore, 154 laboratory tests have been performed to investigate the thermal conductivity of quartz sands with different gradings, including continuous gradings with various uniformity coefficient (2–10.6) and mean particle size (0.25–1.33 mm) and gap gradings with different fine content (0–100%), size ratio (2.7–9.5), and uniformity coefficient of coarse particles (1.3–3.9). The result indicates that the variation of thermal conductivity with grading is inversely related to the change of void ratio with grading at the same initial state. For a given void ratio, the thermal conductivity of the continuously graded sands is affected by both the uniformity coefficient and mean particle size. Besides, the thermal conductivity of the gap-graded sands varies with fine content and size ratio, but has no significant correlation with the uniformity coefficient of coarse particles under the fine-dominated structure. Based on the experimental data in this study, an empirical model is formulated for dry quartz sands with broad spectrum of grading. The model has only three physical parameters (representative particle size and limiting void ratios), which can be readily determined from conventional laboratory tests. The error of the proposed model is basically less than 10% and 20–25% for crushed and natural quartz sands, respectively, indicating that this model is effective for quartz sands with a broad spectrum of grading and wide range of void ratio.