Analysis of Heat Pulse Measurements in Double-Layered Soils with the Heating Probe Positioned at the Layer Interface

A heat-pulse (HP) sensor installed in a double-layered soil with the heating probe positioned at the layer interface violates the underlying assumption of soil homogeneity for the cylindrical perfect conductors (CPC) theory used to interpret the HP data. In this study, laboratory and numerical experiments were performed to evaluate the heat transfer patterns and models to analyze HP measurements when the heating probe was positioned at the interface of a double-layered soil with different upper- and lower-layer properties. Built on the Philip and Kluitenberg (1999) concepts, a parameterized hetero-CPC theory was developed to describe temperature rise with time curves at the sensing probes in the upper and lower soil layers. The hetero-CPC estimates matched well to the simulated values, and its accuracy relied on the thermal property differences between the upper and lower layers. The heat distributions caused by heat pulse inputs in a layered soil showed semi-circular isotherms with different radii centered on the heating source, and the maximum difference between heat fluxes in the upper and lower soil layers was about 60 W m -1 in the studied scenarios. The proposed hetero-CPC model was able to accurately account for the combined effects of finite probe properties and heterogeneous soil thermal property values in a double-layered soil system