Air convection within coarse rock-fills enhances winter-time heat extraction from underlying soils. Modeling this phenomenon requires the knowledge of intrinsic permeability. This study focuses on the measurement of intrinsic permeability using natural air convection within a 1 m3 test cell. Upward heat flow conditions are applied to various specimens. Test results are analyzed using a theoretical solution of natural convection in a square enclosure. Four materials were studied, with effective particle sizes (d10) ranging from 90 to 150 mm and porosities ranging from 0.37 to 0.41. The results showed that intrinsic permeability increases with increasing d10. The experimental results were adequately predicted by the Kozeny–Carman and Chapuis equations. Only slight deviations were observed, which is considered acceptable given that these equations were developed for materials with much smaller values of d10. The experimental results of this study confirm the value of intrinsic permeability recently used in a study of natural convection within a rock-fill dam in northern Quebec, Canada.

International audienceAn optical sensor was designed to measure the fine solid particles concentration contained in a fluid flow. Thissensor is composed of four light-emitting diodes and four associated light-dependent resistors, allowing the measurement offluid transparency. Given the small device dimensions, it can be placed close to the particles exit from the specimen. Theoptical sensor is able to instantaneously measure a large range of clay or silt concentrations in the effluent, without a significantinfluence of flow rate. The presence of sand grains in fluid flow can be detected. The use of this sensor with a specifictriaxial device allows precise characterization of the initiation and development of the suffusion process on clayey sandspecimens. It is shown that suffusion of clay particles induces a decrease of hydraulic conductivity, which is due to a diffuseprocess of eroded particles filtration. Clay suffusion and filtration processes are influenced by grain-size distribution andalso by grain shape of the coarse fraction. Under a high hydraulic gradient, clay suffusion can be accompanied by sand erosion.The critical value of mean pore velocity to initiate clay suffusion was determined for the types of soils

This paper presents an experimental study on thermal radiation and the thermal conductivity of rock-fill materials using a 1 m × 1 m × 1 m heat transfer cell. Testing temperatures are applied by temperature-controlled fluid circulation at the top and bottom of the sample. Heat flux and temperature profiles are measured to establish the effective thermal conductivity λe, which includes contributions from both conduction and radiation heat transfer mechanisms. The materials studied had an equivalent particle size (d10) ranging from 90 to 100 mm and porosity (n) ranging from 0.37 to 0.41. The experimental results showed that thermal radiation greatly affects the effective thermal conductivity of materials with λe values ranging from 0.71 to 1.02 W·m−1·K−1, compared with a typical value of 0.36 W·m−1·K−1 for conduction alone. As expected, the effective thermal conductivity increased with particle size. An effective thermal conductivity model has been proposed, and predictions have been successfully compared with the experimental results. Radiation heat transfer becomes significant for d10 higher than 10 mm and predominant at values higher than 90 mm. The results of the study also suggest that the cooling potential of convection embankments used to preserve permafrost conditions may not be as efficient as expected because of ignored radiation effects.

The thermal conductivity of bitumen concrete is a key parameter in the thermal analysis of pavements submitted to widely varying climate conditions. This paper presents the experimental results of thermal conductivity of bitumen concrete typically used in the Province of Quebec. The results show that the thermal conductivity of bitumen concrete is dependent on the aggregate's mineral origin and on the amount of air voids. It is also shown that the presence of bitumen increases thermal conductivity compared to unbound aggregates. The paper demonstrates that the effect of bitumen creates thermal bridges between aggregate particles similarly to other types of binders such as Portland cement and natural binders found in sedimentary rocks. Based on these observations and on the analyses of over 80 data sets from the literature, an existing model is used to develop a simplified thermal conductivity equation to estimate this parameter for bitumen concrete.

On page 681, eq. [6] should read: ½6 q "¼ rTl e 1:735 ln gbCH 2 rTK nl e À 5:38

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