Volcanic Soils: Inverse Modeling of Thermal Conductivity Data

Abstract

Volcanic ash soils are formed from ash and cinder deposits that largely consist of non-crystalline minerals, volcanic glass and organic matter. Their application to engineering ground technology requires a thorough knowledge and good understanding of their historical formation, structure, mineralogy and thermal and hydraulic properties. Consequently, inverse modeling was applied to the thermal conductivity (λ) data of 22 soils from Hokkaido (northern Japan). A large majority of these soils contained volcanic ash that markedly influenced their physical properties. For example, 11 natural soils (volcanic, highland and lowland soils) had average λ values of 0.14 W·m−1·K−1 and 0.52 W·m−1·K−1 at dryness (λdry) and saturation (λsat), respectively. The inverse modeling of λ data revealed that the average λ values of soil solids (λs) and volcanic glass (λvgl) were about 0.48 W·m−1·K−1 and 0.25 W·m−1·K−1, respectively. The influence of organic matter on λs was found to have a minor effect. A reverse analysis of saturated frozen soils revealed that, at − 5 °C, about 87 % of water was converted into ice, i.e., unfrozen water content (θun-w) ≈ 0.13.