In the first half of 2011, a sewer was rehabilitated in downtown Berlin, not far from the Kurfürstendamm. The rehabilitation of a 1,230 m section of the oval sewer in the Düsseldorfer Straße, from the Brandenburgische Straße, up to the Hohenzollerndamm became necessary due to leaks, incrustations and tree root intrusions.

Due to the special product characteristics, the use of peroxides in the resin could be omitted for the curing even though the walls were quite thick. This allowed for a great degree of flexibility at the construction site.

In order to reduce the inconvenience for the local residents and traffic in the inner-city area, the Berlin water utility called for tenders to rehabilitate using Trenchless Technology. For Karl Weiss Technologies GmbH, who won the bid, this presented a great – but challenging – opportunity.

Division Manager for sewer rehabilitation at Karl Weiss and Site Manager for the Berliner rehabilitation project Bernd Wiese said “On the one hand, the dimension DN 600/900 mm oval sewer is something special. On the other hand, the length of over 1.2 km is a size that you don‘t see every day.”

Foreman for the project Mario Montag said “The installation of an oval profile is more difficult simply because most of the sewers are steeper. The demands on the construction crew are clearly higher here than with a circular profile.”

An elevating challenge

The water drainage proved to be a particular challenge for this project. The water conduit, which ensured the drainage and was originally planned to be rehabilitated on the pavement, had to be constructed at an elevation of 5 m instead to minimise the inconvenience for pedestrians during the rehabilitation work.

Upon completing the first construction section of the provisional 500 m pipeline, which was equipped with a pump station, the entire system was dismantled and then reassembled at the second rehabilitation section. The site also required a high degree of organisation and logistical expertise due to the construction site being located in a central traffic-related area.

Mr Wiese said they were also trying to achieve minimal disruption for local residents: “Even if there is hardly any noise during trenchless sewer rehabilitation, we still need the understanding of the local residents. That is why we carried out the actual rehabilitation work only two workdays in the week.”

In order to utilise these days time-wise, a special permit was needed from the city administration.

No hybrid curing

The material for the individual rehabilitation sections of 80–150 m lengths was produced by the liner manufacturer, Brandenburger from Landau, and was delivered ready-for-installation. As storage is mandatory in Berlin, the liner had to be available on-site for the entire construction project.

Pipe liners with a wall thickness of 11.9 mm were required for the rehabilitation due to the condition and the statics of the sewer in the state of old pipe I. The installation of a peroxide liner was necessary, because at a wall thickness of over 10 mm, the curing is not ensured to the outer liner edge by only UV light and without an additional heat-curing catalyst (hybrid or combination curing) on many liner products.

As the project was located in the heart of Berlin, this process was out of the question for Karl Weiss. Storage for GFRP pipe liners can be quite expensive and complicated because of the additional catalyst for the curing needing to be cooled continuously. The construction sites need to be precisely planned and the liners have to be installed directly out of the cooling wagon. In addition, to prevent a curing reaction due to the warm pressurised air during the erection of the liner, a cooling pipe needs to be employed during the installation itself. Problems can arise quickly when there are delays on the construction site or there are changes in the planning.

Seeing the light

In Berlin, the sewer rehabilitation in Wilmersdorf could nevertheless be executed exclusively with light-curing GFRP liners. Ensuring a complete curing, the development of pipe liners from Brandenburger is advanced so that the resin is triggered to react by pure UV light even at greater wall thicknesses.

Director of the order processing centre at Brandenburger Philipp Bergmann said “This lies, on the one hand, in the special wound liner structure of the Brandenburger liner and, on the other hand, on the transparent resin-glass compound. This way, the UV rays enter the material structure deeply and evenly for the curing. A curing of the liner up to a wall thickness of 12.6 mm is thus possible without peroxide.”

According to Mr Bergmann, construction sites have already successfully completed curing pipe liners with a 13.3 mm wall thickness. According to manufacturer specification, to certify the complete curing, with greater wall thicknesses, the speed at which the nine-unit UV light chain, each with 1,000 watt output, runs through the liner has been set to 40 cm/min. The curing time on construction sections of 100 m lengths, an average realised in Berlin, took about four hours.

For the sewer rehabilitation on the Düsseldorfer Straße, this was a logistical and economical advantage. In comparison to using a peroxide liner, the new BB plus liner from Landau allowed the rehabilitation work in the middle of Berlin to be as flexible as possible, and made the cost of transport and storage significantly more beneficial.

Even for complicated projects that require liners with a greater wall thickness, the development of the UV-curing GFRP pipe liner has made it possible for trenchless sewer rehabilitation without hybrid or combination, as proven at the Berlin Wilmersdorf project.