Thermal and electrical response of unsaturated hydrophilic and hydrophobic granular materials

The thermal and electrical properties of unsaturated soils have been less investigated, compared with geomechanical characteristics, despite the wide range of engineering implications. Moreover, the wettability of soil surface commonly accepted in unsaturated soil mechanics is often assumed to be wettable, whereas water-repellent (hydrophobic) soils can exist in natural systems. This study presents the synthesizing method of water-repellent soils and experimental procedure to evaluate the evolution of thermal and electrical properties of unsaturated wettable (hydrophilic) and water-repellent (hydrophobic) soils. Sands are chemically treated with an organic silane to make the particle surface water-repellent. The transient plane source method is used to obtain the thermal conductivity of both hydrophilic and hydrophobic specimens. The electrical conductance is measured by the two-electrode system as well. The degree of saturation varies for both experimentations to assess the surface wettability effect that is captured by thermal and electrical conduction. The different capillarity, driven by surface wettability of soils and corresponding spatial distribution of water phase in pore space, influences thermal and electrical properties for tested specimens. The synthesis of hydrophobic soils in conjunction with simple experimental techniques enables one to evaluate physical properties of unsaturated soils at the particle-scale.