SITE VISIT TO AMPRION
Renewable electricity generated by offshore wind turbines must first be transported to the coast and from there further inland. This places new demands on the transmission grid: new lines must be built to meet the increased transport requirements – both overhead lines and underground cables.
The necessary construction measures are divided into several projects and project phases at Amprion, for example: The EnLAG project No. 2 from Ganderkesee (Oldenburg district, Lower Saxony) to Wehrendorf (Osnabrück district, Lower Saxony) is followed by project No. 16, which comprises the necessary line expansion for the route from Wehrendorf via Lüstrigen to Gütersloh in North Rhine-Westphalia. There is one special feature here: EnLAG project no. 16 was designated by the legislature in 2016 as a pilot project for partial underground cabling.
Partial cabling in Borgholzhausen
We know all about water flows. However, it is our experience in civil engineering that has qualified us, as civil engineers from the water management sector, as project partners of Amprion for the kilometers of power lines that are being built as underground cables around the urban center of Borgholzhausen as part of the EnLAG project No.16.
Partial cabling in Borgholzhausen
We know all about water flows. However, it is our experience in civil engineering that has qualified us, as civil engineers from the water management sector, as project partners of Amprion for the kilometers of power lines that are being built as underground cables around the urban center of Borgholzhausen as part of the EnLAG project No.16.
Gentle hills with a 40% incline
Before we were able to visit the construction site in person, we had to climb a steep hill! This is also a challenge in this project: the cable route runs over two “gentle” hills – the Riesberg and the Hengberg. The grid expansion in Borgholzhausen is one of a series of pilot projects in which the trigger criteria for testing underground cabling may be applied, so that if the result is positive, an extra-high-voltage line can be installed as an underground cable on technically and economically efficient sections and supplement the construction of overhead lines. In this case, for example, the town of Borgholzhausen and a citizens' initiative had spoken out in favor of underground cabling.
Gentle hills with a 40% incline
Before we were able to visit the construction site in person, we had to climb a steep hill! This is also a challenge in this project: the cable route runs over two “gentle” hills – the Riesberg and the Hengberg. The grid expansion in Borgholzhausen is one of a series of pilot projects in which the trigger criteria for testing underground cabling may be applied, so that if the result is positive, an extra-high-voltage line can be installed as an underground cable on technically and economically efficient sections and supplement the construction of overhead lines. In this case, for example, the town of Borgholzhausen and a citizens' initiative had spoken out in favor of underground cabling.
The 4 km long underground cable route is located in the areas of the old overhead line and is essentially 25 meters wide and approx. 2 meters deep. That is over 100,000 m3 of earth moved, which means a lot of responsibility with regard to the ecological impact. During the planning phase, a soil protection concept was developed to define all necessary measures before construction began, thereby maintaining soil functions and restoring them once construction was complete.
The 4 km long underground cable route is located in the areas of the old overhead line and is essentially 25 meters wide and approx. 2 meters deep. That is over 100,000 m3 of earth moved, which means a lot of responsibility with regard to the ecological impact. During the planning phase, a soil protection concept was developed to define all necessary measures before construction began, thereby maintaining soil functions and restoring them once construction was complete.
Soil protection concept
- Most of the excavated soil is stored on site.
- The soil horizons are returned to the same place after the empty pipes have been laid.
- The empty pipes are laid in the liquid soil without additional formwork.
- The liquid soil is produced near the construction site.
- Liquid soil has low final strength and remains easy to remove even after setting and hardening: it can be removed with a spade or loosened with a hoe.
- Liquid soil can be pumped and thus distributed in steep areas using pumps.
Unfortunately, liquid soil is liquid.
Filling trenches on slopes with liquid soil is no easy task without formwork: not only does the soil tend to flow downhill, but the empty pipes are also at risk of floating. It's a good thing we have an experienced construction company on the project team. After a few tests, the necessary tools were designed and the timing of the men on site was perfectly coordinated: the specially manufactured buoyancy protection for the empty pipes remains in the trench until the liquid soil has set just enough. Then the steel struts are removed so that only soil fills the pit at the end.
Unfortunately, liquid soil is liquid.
Filling trenches on slopes with liquid soil is no easy task without formwork: not only does the soil tend to flow downhill, but the empty pipes are also at risk of floating. It's a good thing we have an experienced construction company on the project team. After a few tests, the necessary tools were designed and the timing of the men on site was perfectly coordinated: the specially manufactured buoyancy protection for the empty pipes remains in the trench until the liquid soil has set just enough. Then the steel struts are removed so that only soil fills the pit at the end.
Desk vs. construction site
On-site visits are important for our engineers and draughtsmen. On screen and on paper, it is easy to lose sight of the dimensions we work with in-house and the challenges that await us during the implementation of a project. Marius Graskamp, who is responsible for construction management on site, made the visit to the construction site in Borgholzhausen possible for us. We would also like to send a big thank you to Amprion.
Desk vs. construction site
On-site visits are important for our engineers and draughtsmen. On screen and on paper, it is easy to lose sight of the dimensions we work with in-house and the challenges that await us during the implementation of a project. Marius Graskamp, who is responsible for construction management on site, made the visit to the construction site in Borgholzhausen possible for us. We would also like to send a big thank you to Amprion.
