Volcanic Soils: Inverse Modeling of Thermal Conductivity Data

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 ( λ dry ) and saturation ( λ sat ), respectively. The inverse modeling of λ data revealed that the average λ values of soil solids ( λ s ) and volcanic glass ( λ vgl ) were about 0.48 W·m −1 ·K −1 and 0.25 W·m −1 ·K −1 , respectively. The influence of organic matter on λ s 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 ( θ un-w ) ≈ 0.13.