Field Studies on the Influence of High‐Voltage Direct Transmission Underground Cables on Soils Along the SuedLink Route in Southwest Germany

ABSTRACT Background The SuedLink was planned as a high‐voltage direct‐current underground cable route. The construction itself is a massive intervention on soil, and during operation, the power cables emit up to 32 W of heat per cable meter at maximum load. Aims The study aimed to investigate the impact of the construction and the heat emission of the SuedLink on soils typical of Southwest Germany. Methods Four test sites, each covering approximately 0.6 ha, were established following best practice along the planned SuedLink route in 2021. Each test site was set up in a fully randomized split‐plot design. Heating pipes were installed at a depth of 1.5 m with a target heat emission of 32 W per meter of cable. Each test site was extensively instrumented with temperature, heat flux, and soil moisture sensors. Results Temperatures 5 cm above the heating pipes at a depth of 1.25 m were 14–16°C higher than the control. In the heated plots, soil temperatures in the center of the plowing horizon at 0.15 m depth were 1–3°C higher than in the control soil. The strip affected by the heat emission had a width of about 10 m. Negative impacts on bulk density, plant‐available water, and air capacity were not observed. Conclusions During regular operation at a load ≤75%, the average increase in temperature in the plowing horizon at a depth of 0.15 m is expected to be less than 1.6°C in the soils along the SuedLink route in Southwest Germany.