Thermal properties of sandy and peat soils under unfrozen and frozen conditions

Abstract

In situ measurements of soil thermal properties are frequently required when studying coupled heat and water transfer in soils. While these values are widely available for mineral soils, but not for organic-rich peat soils. This study aimed at measuring the thermal properties of six peat:mineral mixtures collected from an oil sands mine reclamation study site using a dual-probe heat-pulse (DPHP) method. The soil mixes were tested across a range of water contents (θ) and bulk densities (ρ). Generally, compared with the thermal conductivity (λ) of sand soil, λ of peat soil subsequently decreased with increasing peat:mineral ratios and increased slightly with the increase of θ, indicating the significant impact of organic matter. Similar to λ, the heat capacity (C) decreased with the increase in soil organic matter content, and the decrease in θ and ρ, but differences were relatively small between the different soil mixtures. With increasing θ, λ increased exponentially, but C increased linearly. At all temperatures but between −2 °C and 0 °C for sandy soils and −4 °C and 0 °C for peat soils due to ice melting, the de Vries thermal conductivity model described the measurements very well and the DPHP method is suitable to measure the real soil thermal properties. The measured thermal properties for the peat soil can be used in modeling heat conduction in a high latitude cold area, and is a prerequisite for designing peat soil cover in reclamation soil.