In analytical and numerical calculations of the underground cable ampacities in accordance with the relevant IEC standards and the IEC technical report, it is usually assumed that the native soil, cable bedding, and other materials used in and around cable trenches are homogeneous, although this is not the case in reality. This paper, however, assumes that the native soil consists of two horizontal layers with different thermal conductivities. The upper native soil layer includes soil material as well as shrinkage cracks between the ground surface and the horizontal plane where the reference soil temperature is measured, whereas the lower native soil layer includes only soil material below t... More >