Thermal conductivity characterisation of shallow ground via correlations with geophysical parameters

Abstract Thermal conductivity is an important physical property of geological formations. For example, a comprehensive assessment of the thermal conductivity variations in the shallow ground surrounding a heat exchanger borehole can be used to determine the installation parameters of a ground-source heat pump. However, in some locations, it is not possible to measure thermal conductivity directly. One of the most common methods to indirectly infer thermal conductivity is to establish correlations between thermal conductivity and various geophysical parameters. By utilising test data acquired from drilling sites and ascertaining the corresponding geophysical parameters via non-invasive geophysical methods, such correlations can be obtained. At 11 test sites, the thermal conductivities were measured in situ via thermal response testing, and the corresponding values for the S-wave velocity and density were calculated using the Microtremor survey method (MSM). The correlations between the thermal conductivity, S-wave velocity, and density in the tested shallow ground were built by exponentially fitting. By utilising the launched correlations, two-dimensional (2D) cross-sections along the microtremor survey line were created to illustrate the thermal conductivity variations in the shallow ground. These results demonstrate that this approach can be used to infer the thermal conductivities of areas that cannot be tested directly.