Reduced-scale physical modelling of energy walls in partially saturated soils

Energy geostructures are often designed assuming fully saturated or dry soil conditions, although their shallow depth frequently implies interaction with partially saturated soils. Under these conditions, soil thermal and hydraulic properties depend on moisture content, and temperature gradients induced by thermal operation may activate moisture migration, affecting heat transfer. Experimental evidence addressing these coupled thermo-hydraulic processes remains limited, particularly for energy walls. This paper presents a laboratory physical model of a reduced-scale energy wall embedded in partially saturated, uniform sand. The setup allows controlled investigation of heat exchange, temperature gradients, and moisture redistribution under imposed thermal loading. Soil thermal conductivity and hydraulic properties were characterized under unsaturated conditions to support test interpretation and future numerical modelling. Preliminary heating tests show expected temperature gradients with distance from the wall and time-dependent thermal response, while moisture variations appear very limited and delayed. A verification on the possible influence of soil–atmosphere interaction on moisture evolution at shallow depths is recommended. Although not intended to reproduce field-scale behaviour quantitatively, the model may provide benchmark data for validating coupled thermo-hydraulic numerical simulations and improving prediction of energy wall performance in partially saturated soils.