Parameters for the design of HDD installed power cables in soil and rock

When operating buried power cables, the mechanical and thermal properties of the cable bedding need to meet certain requirements. On the one hand, positioning and protection of the cable and protection pipe from mechanical stress demand mechanical stability. On the other hand, electric losses during transmission result in thermal energy that needs to be dissipated. Since the ampacity of the cable depends on the maximum permissible temperature of the conductor, the potential load of the power line is directly connected to the thermal properties of the bedding. To avoid accelerated aging or even damaging of the cable, an adequate assessment of the cable bedding is essential to ensure a safe long-term operation within the mechanical and thermal limits. While an underground cable route is typically realized using cable trenches, intersection points with existing infrastructure (e.g. roads, railway network, inland waters) need to be crossed under using engineering methods like horizontal directional drilling (HDD). Since one segment of the cable route with poorer bedding properties would reduce the potential load of the whole power line, the backfill materials used to fill the space between protection pipe and borehole wall also have to be designed to meet the requirements mentioned. In this contribution, laboratory investigations are discussed, which can be used for the design of adequate backfill materials considering important subsoil properties.