The city of Peine in Lower Saxony lies in a sandy heathland between Hanover and Braunschweig. In the “Dungelbecker Bruch” landscape conservation area on the outskirts of the town’s Dungelbeck district the inlet pipes to the wastewater pump station needed to be renewed for hydraulic and construction reasons. Due to space limitations – the entire length of pipeline runs through a landscape conservation area, parallel to a trench – it was decided to install the vitrified clay pipes by means of controlled pipe jacking.
Landscape conservation a chief argument
Controlled pipe jacking and slurry tunnelling seemed a suitable solution, as
- other operating sewers ran parallel to the planned new route
- the groundwater levels partially reached above ground level, and
- the pipe route had to run beneath an enclosed marsh.
The marshland forest, an allocated landscape conservation area, made access to the planned route difficult to virtually impossible.
The location within the conservation area itself allowed only for underground installation of the supply pipes (image 1).
Installation in groundwater
The first wastewater pipeline was pressed with DN 400 vitrified clay jacking pipes in three sections of 123 m, 133 m and 39 m in length. DN 1200 vitrified clay jacking pipes for the combined sewers were pressed parallel to this pipeline (image 2). Here, the longest pipe jacking section was just under 260 m, which was easy to achieve without a blind shaft. Due to the length of the entire route, a lost intermediate jacking pit with intermediate flow and tracking pipes was installed; but as the jacking forces were so low there was no need to activate it (image 3). A second stretch was 43 m long.
As expected, the gravel/sandy soil did not pose any major problems for the pipe jacking. Pipe floors reached to a depth of around 3.60 m, the average cover size was 1.70 m. The initial excavation and reception pits were made as closed sheet pile boxes. To protect against groundwater penetration, the floor areas around the inlets and outlets were gelled (image 4).
All-round landscape conservation
In all, the construction project took 14 months to complete, of which around eight months were needed for the pipe jacking. As vitrified clay pipes are made of natural raw materials, are neutral to soil and groundwater, and environmentally friendly and recyclable, the citizens of Peine now have new supply pipes seamlessly integrated into the landscape conservation area.
Income from wastewater taxes will amortise the total costs of approx. €1.8 m. Based on the 80 year amortisation period, the financing was justifiable.