Munich
Großlappen sewage treatment plant
Munich, Germany / 2024
A new plant for the thermal recovery of sewage sludge is being built on the site of the Gut Großlappen sewage treatment works in the north of Munich. As part of the expansion, existing pipe networks are being extended and additional supply connections are being established. PORR special civil engineering München, acting on behalf of the PORR Saaldorf-Surheim branch, was responsible for constructing a watertight construction pit for the creation of a new underground service duct. The associated construction and excavation planning was carried out by PORR special civil engineering Planung.
Facts & Figures
Company
PORR Spezialtiefbau GmbH
Type
Turnkey construction pits
Runtime
2024
Watertight construction pit for a 115-metre-long service duct
New infrastructure beneath the sewage treatment works site
The Gut Großlappen sewage treatment works is one of Munich’s two municipal sewage treatment works. As part of the expansion, additional facilities for the treatment and recovery of sewage sludge are being built. With the new facilities, the need for supply and disposal pipelines is also increasing. These run within accessible service ducts, which connect the various parts of the plant and allow access for inspection, maintenance and operation. The new service duct is approximately 115 m long, lies about 6.5 m below ground level and has internal dimensions of 4 × 4 m.
Watertight construction pit in the groundwater zone
An excavation pit up to 9 m deep was dug to construct the duct. As the groundwater level was in some places one to two metres above the bottom of the construction pit, a watertight design was required. To achieve this, PORR special civil engineering constructed around 200 m of overlapping bored pile walls. A total of around 3,300 metres of drilling was carried out. The bored piles reached diameters of up to 880 mm and lengths of up to 13.5 m. This laid the foundation for the subsequent sewer and structural works within the sewage treatment works site.
Work between existing and new structures
The new service sewer connects to existing underground structures at the sewage treatment works. Additional specialist civil engineering works were required in these connection areas. The underpinning of existing structures as well as the construction of the connections were carried out using the jet grouting method (JGM). In addition, JGM sealing columns were constructed. In areas with underground installations susceptible to settlement, sleeve pipe injection columns were also used to seal individual connection points.
Construction in water-bearing subsoil
The geological conditions at the site determined how the drilling work was carried out. In deeper areas, individual bored piles encountered water-bearing sand layers. Consequently, these piles were driven under water pressure. At the same time, sections of the construction pit were temporarily secured as well as braced using 4-strand anchors as well as I-beams and pipe braces. Step by step, the construction pit for the new service duct was thus created, whilst operating within the constraints of a functioning sewage treatment works site.
The foundation for the new plant infrastructure
Even before the new plant structures become visible, the connections between the individual areas of the sewage treatment works are taking shape beneath the ground surface. The construction of the construction pits, the construction of the bored pile walls, as well as the ground stabilisation and grouting works have laid the groundwork for the construction of the new service duct. This marks the completion of a further section of the technical infrastructure at the Gut Großlappen sewage treatment works.
