The borehole resistance is determined as a measured value in the so-called Thermal Response Test (TRT), which is carried out as a test on a geothermal probe at the planned plant location.

The borehole resistance consists of a value that is influenced by the probe geometry, the thermal properties of the grouting material and the influence of disturbances (possibly existing groundwater). Thermally improved grouting materials are favourable because it reduce the resistance of the borehole.