Comparative study on thermal properties of undisturbed and compacted lateritic soils subjected to drying and wetting

Abstract

Soil thermal properties are essential for investigating the thermal performance of many kinds of underground thermal engineering structure. To investigate the influences of microstructure alteration on soil thermal properties, thermal conductivity, thermal diffusivity and specific heat capacity were measured for both undisturbed and compacted lateritic clay specimens subjected to drying and wetting with the thermal probe method. Results revealed that thermal conductivity and diffusivity of undisturbed specimens were higher than that of compacted specimens. The specific heat capacity of the undisturbed and compacted specimens was roughly the same. For the same volumetric water content, thermal conductivity of specimens produced by drying was higher than that by wetting due to hysteresis effects. Test results from the scanning electron microscope and mercury intrusion porosimetry confirmed that compared with compacted specimens, the undisturbed specimens have a relatively uniform pore system that improves the extent or quality of heat transfer paths through the contact points and water bridges, thus have higher thermal conductivity. The hysteresis effects on soil thermal conductivity can be explained by the ink-bottle effect, effects of pore size distributions induced by shrinkage and swelling, and differences in the volume of entrapped air between drying and wetting.