By Markus Lebek
On the ‘Am Kortelbach’ rehabilitation project, urgent rehabilitation work had to be carried out to a sewer system in the sensitive area around the tracks of a rail station in Unna, a town and county seat in the German state of North Rhine- Westphalia. The project was completed successfully in spring 2022 on behalf of Stadtbetriebe Unna, the municipal utilities company responsible for wastewater management.
This rehabilitation project presented a number of particular challenges including: The conditions for digging a trench, which were made harder by changes of direction and a change of profile; the dire condition of the existing pipe; holding back the wastewater and thus also the safety of personnel; and the size of the liner at DN1800.
The company tasked with the trenchless rehabilitation, the Gelsenkirchen branch of DIRINGER & SCHEIDEL ROHRSANIERUNG GmbH & Co. KG, opted for proven UV liner technology and an Alphaliner from RELINEEUROPE and the RELINE UV Group. The civil engineering work was entrusted to Lage-based SMG Bautenschutztechnik GmbH, which developed a technique specifically for this task in order to create the right geometry for laying the liner. The professional cooperation between everyone involved was one of the main reasons the project was able to be completed successfully within the tight timeframe, despite all its non-standard requirements.
Dipl.-Ing. Thomas Matter, Head of Wastewater Management/Water Bodies at Stadtbetriebe Unna, explained: “The Kortelbach is a stream that rises in a part of south Unna known as Billmerich. As it flows north, it crosses two retention basins. Up until 2019, the stream flowed into a pipeline about 2 km long when it reached the town centre. From here, the stream water was mixed with combined wastewater, and the stream running inside the pipeline became a sewer for combined wastewater. Between 2016 and 2019, the clean stream water was separated from the combined wastewater. Stadtbetriebe Unna constructed a pipeline about 2 km long for the watercourse, using the manned pipe jacking method. After this work was complete, the combined wastewater sewer under the tracks in Unna station had to be strengthened. The existing profile of the Kortelbach stream had been steadily lengthened over the years, and the expansion of the railway station meant that the sewer system had to be adapted accordingly also. The profile comprised a square about 1.90 m wide with a semicircle on top. The bottom of the sewer contained a large number of flaws, and the masonry joints had been eroded along the entire length of 120 m and would have required extensive renovation. On the south side of the station complex, in the inlet section, the sewer changes direction by about 12°. As this change of direction lies within the station site, it would not have been possible to lay a trench. At the same time, access via the northern side is severely restricted due to a change of profile. Overall, holding back the wastewater, and therefore personnel safety, posed the biggest challenge to rehabilitating the existing profile.”
Various rehabilitation options were investigated in light of the limiting conditions mentioned previously. As Thomas Matter explained: “We did this together with Pipefocus, an engineering firm based in Krefeld, and plumped for laying a new pipe using the jacking method as our way of crossing the tracks. However, the land that we needed along the planned course of the pipeline was not available. It would not have been possible to lay a winding pipe due to the route situation and profile accessibility described. Installing individual segments proved unfeasible, and laying a water-cured liner was not an option either. A measurement of throughflow rates over the previous few months suggested that 10 l/s was discharged at night during dry weather, while heavy rain generated a combined wastewater flow of 4,800 l/s. The liner needs about a week to heat up. As it is not possible to forecast the weather conditions for the whole of this heating-up period, so this was discounted also. Laying a UV liner appeared unfeasible due to the change in direction in the pipe’s route and was initially not pursued any further as an option.”
A potential solution first began to emerge when Stadtbetriebe Unna brought two other companies into the planning process for the sewer rehabilitation. Lage-based SMG Bautenschutztechnik für Hoch- und Tiefbau (SMG) contributed its planning and execution expertise for converting and profiling the square profile into a DN1850 half-shell, while the Gelsenkirchen branch of DIRINGER & SCHEIDEL ROHRSANIERUNG (D&S) formulated the conditions for a light-cured liner from the user’s perspective. The planning was underpinned by a laser scan provided by the Dresden-based surveyors Geokart.
Deploying tailored UV-light-cured technology
First of all, the team from SMG had to prepare the sewer to be rehabilitated. SMG’s CEO, Dipl.-Ing Volker Schmidt, described a tricky situation: “The laser scan showed us that the Kortelbach varied in width between 1.80 m and 1.90 m and in height between 1.92 m and 2.27 m. In addition, a DN400 grey-cast-iron pipeline laid inside the sewer cut around 500 mm into the bottom area. Factoring the ideal geometry of a liner into the laser scan produced a maximum installable cross-section of DN1800. It became clear that the bottom had to be raised from its current level across the board. A height difference of some 600 mm had to be compensated for at the deepest point. Debris and boulders had been deposited at the bottom of the sewer over time, some of which were the diameter of a medicine ball. The task in hand was thus obvious, clear the deposits, remove the DN400 grey-cast-iron pipeline, re-level the bottom, and lay a DN1800 channel along it in a half-shell shape.”
Using a conveyor belt, the UV liner then had to be drawn into the manhole and into the sewer section to be rehabilitated. The integrated anti-slip film and integrated pre-liner protect the liner against heavy mechanical loads during draw-in, providing ideal conditions for inserting it into the sewer. On the ‘Am Kortelbach’ project, the trench that was dug for draw-in and secured accordingly ran to a depth of 6 m.
“Our hose liner technology has already proven its worth many times over for rehabilitation projects of this kind, and we often work together with RELINEEUROPE in terms of the liner to be laid.” said Dipl.-Ing. (FH) Richard Mohr, CEO of DIRINGER & SCHEIDEL ROHRSANIERUNG.
“The Alphaliner is a GRP hose with an extremely flexible design. Combined with our innovative UV curing technology, which we used here in partnership with our Italian sister company ROTECH, this proved ideal for this unusual rehabilitation project with all its tough challenges that had to be overcome when laying the liner.” Richard Mohr added.
D&S planned the trenchless sewer rehabilitation using an Alphaliner 1800H UP, which was developed to rehabilitate large profiles. For this Alphaliner, a specially formulated polyester resin is used that offers unbeatable resistance to municipal wastewater (UP; classified as Group 4 in accordance with DIN EN 13121; DIN 16946-2 Type 1140; DIN 18820 Group 3).
The ECR glass fibres used are especially resistant to corrosion. The Alphaliner is designed for high structural resilience, enabling very large sewers in particular to be rehabilitated cost-effectively. The rehabilitation process produces an extremely robust liner pipe that can even withstand extreme structural and dynamic influences.
The Alphaliner has been approved by all the relevant international approval bodies (including the Deutsches Institut für Bautechnik (DiBt) in Germany, CSTB in France, QUIK in Switzerland, the WRc in the U.K., and ASTM1216/ ASTM2019 in the U.S.). The Alphaliner 500G UP and Alphaliner 1800H UP variants boast outstanding mechanical properties, meaning that they fulfil all material quality requirements and can withstand the greatest possible structural loads despite relatively thin walls.
The Alphaliner UP UV-light-cured GRP hose liner allows trenchless rehabilitation measures of up to 350 m/day to be carried out particularly fast and efficiently. This minimises disruption for local residents and road traffic, particularly on projects in town and city centres. A rehabilitated section of sewer will have a useful life of at least 50 years.
The main benefits of the Alphaliner UP for municipal wastewater rehabilitation projects include:
- Outstanding chemical resistance to municipal wastewater.
- Strong mechanical properties for long-lasting resilience.
- Unique wear layer on the liner’s inner surface.
- Ideal solution for circular, oval, box-shaped, and custom profiles.
The Alphaliner UP UV-light-cured GRP hose liner ability to rehabilitate up to 350 m/day was especially important with regard to holding back the wastewater for the ‘Am Kortelbach’ project. To minimise water retention time, the liner was designed in a single piece, despite the bend, with a diameter of 1,850 mm, a wall thickness of 10.4 mm, and a total weight of around 30 metric tons. Curing was done using ultra-high-power, high-tech UV REE4000 equipment, which enables the hose liner to cure quickly thanks to innovative lamp technology with a total output of 24,000 Watts.
The curing process was checked and documented online in a continuous process by measuring curing parameters. After carrying out a leak-tightness test and taking a sample from the construction site for the quality test, the ‘Am Kortelbach’ rehabilitation project was able to be completed successfully by connecting the liner ends to the manhole and the Alphaliner to the lateral inlets in line with professional standards.