SPR Europe rehabilitates circulation lines of the treatment plant in Berlin
Often, in addition to cost considerations, site conditions can make open construction impossible. For the rehabilitation of the three 900 mm circulation lines at the Berliner Wasserbetriebe treatment plant in Berlin-Ruhleben, Germany, the constant hydraulic strain of the pipes prompted a decision for trenchless rehabilitation. SPR Europe restored the function and the corrosion protection of the three 80 m long lines with pipe lining with the warm-water curing UNILINER™ process.
Sewer networks are typically upstream of treatment plants, but there are also sewer networks in the plants themselves, sometimes with very large diameters that need to be rehabilitated at some point. Due to their constant hydraulic load, it is clear that when repairs are needed, they cannot be performed using open construction methods. These are perfect conditions for the use of trenchless rehabilitation technology, as in the case of the September 2012 project in the treatment plant of the Berliner Wasserbetriebe in Berlin-Ruhleben, Germany. Here, SPR Europe rehabilitated three parallel 900 mm circulation lines using pipe lining with the warm-water curing UNILINER™ system. The lines cross under the main administration building of the treatment plant, so that no-dig technology was absolutely necessary.
The three circulation lines connect the primary clarifier of the treatment plant with the aeration tanks and have been under full load since their construction. The reinforced concrete pipes in particular suffered from concrete corrosion with some areas of exposed rebar and sporadic deposits. Previously they have been rehabilitated selectively using sealing sleeves. To permanently repair the concrete pipes, the sleeves were removed before installation of the UNILINER™ pipe lining technology. The three lines connect on both sides to the circulation shafts, whose special geometry represented an important parameter for the rehabilitation. Using a light-curing system with a draw-in process was ruled out here for reasons of safety.
From the top edge of the shaft to the lines, inside the shaft a construction height of 8.50 m needed to be surmounted. The overhead shaft was not reachable due to intersecting pipe bridges. The lower shaft, on the other hand, protruded 5 m above the top edge, which also had implications for the implementation of the rehabilitation.
With the UNILINER™ system that was used, a needled felt liner, impregnated with thermo-reactive UP resin, is hydraulically inversed into a blown up "preliner". The liner is then cured by the circulation of warm water. The liner is characterised by an "integral" PE inner coating. A water column above the shaft was built-up to ensure the hydrostatic, tight-fitting inversion of the liner. At the Ruhleben treatment plant, the water column was constructed in circulation shaft 2. From this point, the three pipes were rehabilitated against the direction of flow. An important additional project condition: All circulation lines contained a dimension change from 900 mm to 850 mm. This was accomplished using the UNILINER™, made possible by its longitudinal seam enabling a tailored cone section. Otherwise, it would have been necessary to use a supporting liner, which would then generate an annular space that would need to be dammed.
The circulation shaft that protrudes far above the top edge represented a special challenge for the installation procedure. The use of a conveyor belt, the preferred method for liners of this dimension, was not possible in this case, as at the height and diameter of the shaft, the rolling edge of the conveyor belt could not be positioned precisely over the shaft opening and the liner would have had to be placed on the shaft edge for the feed-in procedure. For this reason, a trapezoidal construction had to be used at the boom of a mobile crane to be able to lower the six-ton liner into the shaft and channel.
For curing the water filling, some 51 cubic metres for each channel was supplied to the liner via a mobile heating system using a circulation system that heated the water according to the exact heating schedule to an inlet temperature of 90 degree Celsius. During the curing procedure, which was measured and documented, the temperature of the liner had to remain above 50 degree Celsius for three to five hours. This led to the complete curing of the liner, as demonstrated by the laboratory remote monitoring of the Ruhleben project and all testing criteria were fulfilled completely.