Main Collector Düsseldorf Centre, Lot 1

The Main Collector centre reorganises the wastewater currents by directing them to the expanded wastewater Treatment Plant South. The section of construction lot 1 consists of two superimposed sewers. The upper part is an egg-shaped combined system sewer which was executed by the tunnel driving technique above the groundwater. Beneath the egg-shaped profile, a circular tank sewer structure with a storage capacity of 25,000 m³ is located completely in the groundwater. According to the regulations currently in force, the combined water has to be treated continuously or must be retained in reservoirs. When certain flow values are reached, the water in the egg-shaped sewer flows out via certain spillway sills in special structures and via down holes to the tank sewer below. For geological and hydrologic reasons, the lower sewer was constructed by the hydro shield method. The sewer is mainly located in quaternary sands and gravels. Individual sections were cut into the tertiary layer. In the course of shield advance, a historic steel bridge of German Rail with admissible settlements up to 5 mm was undertunnelled. For this purpose, a pressure distribution cushion was injected under the foundation. These injection works were carried out from shotcrete shafts via horizontal borings by way of the soil fracturing method. Segmental lining as used in the hydro shield method is suitable only to a limited extent in sewer construction due to higher internal pressures. For this reason, a full round formwork handling rig was used to construct an inner ring for the lower sewer. To create a surface with a low pore-content and to take up the excess water from the concrete, a vacuum was provided in addition to the geotextile fabric in the lower half of the formwork handling rig so as to extract water from the fresh concrete. Owing to this procedure, the quality could be improved significantly.

Country: Germany
Region: Nordrhein-Westfalen
Tunnel utilization: Utilities
Type of utilization: Sewage
Client: City of Düsseldorf, Authority for sewer construction and water engineering
Design: Engineers Metz-Herder-Wendt
Contractor: Hochtief AG, Wayss & Freytag AG, Bilfinger + Berger Bau AG, Philipp Holzmann AG
Main construction method: Trenchless
Type of excavation: Shield machine (SM), mining
Lining: In-situ concrete
No. of tubes: 2
Tunnel total length: 2 x 2,000 m
Cross-section: shield driving 25 m²; conventional tunnelling: 6 m²
Contract Volume: 164 mill. DM
Construction start/end: 1991 till 1996
Opening: 1997