Effect of saturation conditions on thermal properties of sands

Soil thermal conductivity, diffusivity and heat capacity are critical parameters that govern the design of specific geotechnical infrastructure including energy piles, high-voltage cables and pipelines. The presence and flow of water are of particular importance as it dominates the conduction and convection hear transferring mechanisms, leading to a global increase in heat conduction ability by replacing air within the multi-phased soil system. This paper presents preliminary results from an experimental programme that aims to characterise the effects of saturation conditions on the thermal properties of a siliceous sand. Thermal conductivities were investigated for samples prepared to varied relative densities and degrees of saturation by two methods: (Ⅰ) sand-water mixed at specific water contents and moist-tamped in moulds to the target densities; (Ⅱ) cycles of wetting-draining applied to initially dry specimens through a customised test set-up. Thermal needles were employed that trigger transient heat source and monitor temperature variations. Significant differences were observed in the thermal conductivities between the Method Ⅰ specimens and the Method Ⅱ specimens in the first saturation stage. However, the differences diminished in the subsequent infiltration cycles. Overall, the results confirmed strong dependency of sand’s thermal conductivity on saturation conditions as the presence of water envelopes and bridges sand particles in heat conduction.