HV Cable Ratings – Buried in Backfill (Thermal Resistivity)
To achieve the highest possible current rating for buried circuits, cables can be installed in an envelope of material with better thermal heat conduction properties than the native soil. This additional material is referred to as a thermal backfill.
The level of compaction and grain size distribution determines the thermal resistivity of a backfill material. Backfill thermal resistivity should be known (through measurement) to be considered in a design.
The native soil thermal resistivity was increased to 2 K.m/W, and the backfill thermal resistivity value varied from 0.7 K.m/W up to 2 K.m/W