Analysis of heat pulse measurements in double-layered soils with the heating probe positioned at the layer interface

Abstract

In the case where a heat-pulse (HP) sensor installed in a layered soil with the heating and sensing probes positioned at different layers, the HP measurement violates the underlying assumption of soil homogeneity for the cylindrical perfect conductors (CPC) theory that is used to interpret the HP data. In this study, laboratory and numerical studies were performed to evaluate the heat transfer patterns and models to analyze HP measurement data when heating probe was positioned at the interface of a double-layered soil with different upper- and lower-layer properties. A parameterized hetero-CPC model was proposed to describe temperature-by-time curves at the sensing probes in the upper and lower soil layers. The hetero-CPC estimates matched well with the simulated values, and its accuracy relied on the thermal property differences between the soil layers. The heat distributions caused by heat pulse inputs in the layered soils showed semi-circular isotherms with different radii centered on the heating source, therefore showing discrepancies in heat fluxes for the upper and lower soil layers. The proposed hetero-CPC model was able to accurately describe the combined effects of finite probe properties and heterogeneous soil thermal property values on the HP data in a double-layered soil system with the heating probe positioned at the layer interface.