Siphon Dradenau

Approx. 88 % of the domestic sewage of the Independent and Hanseatic town of Hamburg is from 1987/88 onwards conducted from the existing sewerage plant Köhlbrandhöft to the sewerage plant Dradenau and undergoes an additional biological clearing before it is passed into the Köhlbrand. In 1983 the Department for Water Ressources and Sewerage called for tenders for the approximately 2.2 km long connection tube between the two sewerage plants - the Dradenau siphon. Among the propositions offered to underpass the Köhlbrand, the highway BAB A 7 and the Wallershafer harbour, the client decided finally in favour of a shield driving with reinforced segmental lining at a depth of 65 to 85 m. The final design which had been made by the joint venture was preferred not least for safety reasons, because the practically watertight micaceous clay prevailing in this area permitted trouble-free construction of the pipeline without the necessity of using compressed air. The choice of the deep location resulted from the extensive soil explorations which discovered very alternating quaternary soil layers, which form channels down to 60 m depth. Tunnel driving in the quaternary layers would have to be carried out under an air pressure of more than 3 bar in order to keep out the groundwater. Moreover, encountering numerous obstacles would have meant risks for the shield driving which would have been difficult to assess. The connecting siphon which is now in operation works on the principle of communicating tubes and carries the pre-treated water through the deep shafts merely as a result of the static pressure head to the sewerage plant of Dradenau. The construction of the complete structure Dradenau siphon consists of the following components:

construction of the deep shaft Dradenau as start and operation shaft for the shield driving
assembly of the tunnelling machine and approx. 2,220 m shield driving from the shaft Dradenau to the shaft Köhlbrandhöft
construction of the shaft Köhlbrandhöft to serve as a target and retrieval shaft of the shield machine
construction of the in-situ inner concrete lining of the connection pipe starting at shaft Köhlbrandhöft
lining of the shafts in in-situ concrete with a nominal diameter of 3.20 m (Köhlbrandhöft) and 3.00 m (Dradenau) Shield driving.

Due to the chosen depth of the connection pipe, a driving in practically homogeneous micaceous clay could be expected. Since the possibility of encountering water-bearing quaternary channels could not be excluded completely, a tunnelling machine was used which was made for extremely difficult soil conditions. In order to make driving possible also in such areas, this machine, made in Canada, could close the bore head automatically in some seconds with hydraulically operated shutters. Additionally, there was the possibility to remove the conveyor belt behind the tightly closed boring head and to replace it by a pressure tight screw conveyor. All load bearing shield parts were designed for 90 m water pressure.

Technical data:

siphon: length 2,227 m depth underground level up to 85 m
outer segment lining external diameter 4.60 m ring thickness 0.30 m ring width 1.20 m number of segments 5+1
in-situ concrete internal lining clear diameter 3.20 m thickness 0.40 m
tunnelling machine fully mechanized tunnelling machine equipped for underground conversion into an earth pressure balance system made by Lovat, Toronto, Canada
shield machine external diameter 4.75 m length 7.00 m weight 150 t maximum driving force 20 000 kN maximum torque (at 2 rpm) 2,500 kN maximum rotational speed 4 rpm installed power 800 kW.

Country: Germany
Region: Hamburg
Tunnel utilization: Utilities
Type of utilization: Sewage
Client: Freie und Hansestadt Hamburg
Main construction method: Trenchless
Type of excavation: Shield machine (SM)
Lining: Reinforced concrete segments?
No. of tubes: 1
Tunnel total length: 2227 m
Cross-section: Clear diameter 3.20 m
Contract Volume: 400 mill. DM
Construction start/end: ?