At present, Europe’s largest water construction site is situated in the “melting pot” Ruhr district in Germany. The river Emscher with its numerous tributaries not only represents a unique rehabilitation project covering a volume of about €4.5 bn until the end of 2020, but also will provide a new quality of life to approximately two and a half million people living in the entire region between Holzwickede and Dinslaken. A continuous, underground sewer system with a length of about 400 km and a steady slope starting from 8 m up to 40 m below ground level has not been realized in Europe in this way so far. Client is the Emscher-Genossenschaft (Cooperative Society Emscher), Essen, which, in the course of its more than 100 years of history, has often turned out to be a technological pacemaker with ground-breaking innovations regarding wastewater disposal - even far beyond the borders of the Ruhr district.
Concrete mix design for high chemical and static requirements
A recent example is the reconstruction and ecological improvement of the sewage system Sellmannsbach in Gelsenkirchen. Core of the building project is the construction of an efficient storage sewer with overflow at the bottom and the associated manhole structures. For the first time, high-performance reinforced concrete pipes with an inside diameter of 3,600 mm, an outside diameter of 4,320 mm and an overall length of 3.00 m were intended for such a project. In close collaboration between the client and the contractor, Kramer Bauunternehmung GmbH + Co. KG, as well as the pipe manufacturing factory, DW-Werk Dormagen of Berding Beton GmbH, a mix design for these pipes was developed to meet the high chemical and static requirements over a long service life. The outcome is a concrete with an improved acid resistance which meets the resulting further requirements such as the exposure class XA 3 according to DIN EN 206-1 on the basis of the ZTV (Zusätzliche Technische Vertragsbedingungen - Additional Technical Conditions of Contract) “Manufacturing and delivery of sewer pipes made of concrete and reinforced concrete”.
In order to ensure the highest possible quality, the pipes used in Gelsenkirchen of this dimension were furnished with a monolithic dry weather flow channel with a cross section of 1,000 mm already manufactured in the concrete factory of Berding Beton GmbH. It is always reasonable to use such pipes in case of minor dry weather flows or if the flow rates fall during dry weather beyond what is reasonable for the hydraulics. The continuously declining water consumption requires reduced flow cross sections in order to increase the flow rate in our wastewater systems. This is more and more often achieved by dry weather flow channels and customized cross sections. Otherwise there is the risk of biogenic sulfuric acid corrosion as a result of the reduced tractive force. The use of dry weather flow channels can increase the flow rate considerably, but is subject to a channel designed with an accurately fitting, smooth and consistently tight surface.
Transportation and installation especially challenging
Even for a well-organized and experienced team of sewer construction workers, the installation of the precast elements having a weight of up to 38 tons is not like an everyday task and also a logistical challenge, reported site manager, Robin Golchin. As many bridges only allow a clearance height of maximum 4.00 m, the pipes had to be transported in a vertical position. To turn them afterwards back into their laying position, a special anchor was fitted to the pipe crown. Apart from the 250 tons crane to be used for the installation, unloading required another 34 tons tracked excavator for turning the pipes. The pipes for the approximately 320 m long sewer were completely installed in open trench with a depth of cover from 1.50 to 6.60 m above pipe crown for traffic loads of SLW 60 (heavy-duty truck weighing 60 tons) and LM 71 beneath a multiple-track railroad facility. Site manager Golchin is thoroughly convinced, that after careful installation with appropriately precise fitting of the elements weighing many tons, a sewer has been constructed that will survive at least 100 years without any damage and thus meeting the high expectations of the client.