Precast concrete socket pit elements for SuedOstLink network expansion project

SuedOstLink is a high-voltage DC transmission line (HVDC) that is planned to transport renewable energy efficiently – in particular, wind power from northern and eastern Germany to the south of Germany. The line is planned to run from Wolmirstedt in the German federal state of Saxony-Anhalt to Bavaria. The objective is to ensure security of power supply and to replace fossil energy sources. The SuedOstLink, which will run predominantly underground, is an important building block for a climate-neutral power supply system of the future and has already been classified by the EU as a “Project of Common Interest.” The precast concrete specialist Kleihues Betonbauteile GmbH & Co. KG has developed special socket pits at its plant in Sennfeld in Bavaria, Germany, for connecting individual cable segments underground. These elements enable secure, durable connections of high-voltage lines under controlled conditions and are a central component of the SuedOstLink construction project.

The planned power line has a length of approx. 540 km. An essential area is section D3b: it marks the southern end of the SuedOstLink route and runs from freeway A92 (Munich-Deggendorf) up to the Isar Switchgear Station. This section is the final connecting link to the existing network in the Landshut area and enables, by its converter system, feed-in of up to 4 GW transmission capacity. The route has a length of approx. 2 km and contains two powerful converter systems with connection lines to the local transmission grid.

Precisely precast elements

Alexander Mehne, Area Representative of the company Kleihues in southern Germany, explains the project: “For this section, we have designed special socket pits consisting of precast reinforced concrete elements in which the high-voltage DC cable segments can be electrically and mechanically connected. The use of precisely precast concrete elements is ideal here. Kleihues has developed special components for this project, from which the socket pits were assembled.”

These large troughs are made up of easily transported individual elements, into which buoyancy control has already been integrated and which are provided with openings for cable protection pipes. They also feature mounting options for socket supports. For flood protection, flood protection systems, 2 m in height, were necessary on the wall heads of the pits on site.

Installation of the concrete elements, weighing up to 35 tons, took place with utmost precision by the Kleihues installation team using a mobile crane. After splicing, the flood protection systems are dismantled, the pits are backfilled. Thanks to the customized design of the socket pits, these areas can later be used again for agricultural purposes. The advantages of precast construction for the socket pits are obvious: “The pre-manufactured elements enable very fast installation on the construction site, fit perfectly, are reliable, and quickly provide good protection against water ingress,” says Mehne.

The SuedOstLink is expected to be connected to the power supply system in 2027 for the main project (Project 5). The extension (Project 5a) is expected to be fully operational by 2030.