Trenchless Renovation with UV-technology in Austria

Wiener Linien is the municipal transport company of the Austrian Federal Capital, Vienna and is a subsidiary of Wiener Stadtwerke GmbH. It operates the largest regional transport network in Austria, employing around 8.500 people and which transported 939.1 million passengers per year in 2015, making this the sixth largest tram network in the world.

A pipeline, operated by WL and with a bell profile, was found to be defective and the concrete fabric of the pipeline was in poor condition, and so was in need of renovation. Wiener Linien has been awarding contracts to Swietelsky-Faber for sewer renovation for many years.

The rapid implementation of large and special projects as well as the comprehensive expertise and the high-quality execution of the work by Swietelsky-Faber Kanalsanierung are always important decision-making criteria for the award of such special projects. Currently UV lining is one of the fastest and most cost-effective renovation technologies on the market today.

To realise the renovation of the sewer in question Swietelsky-Faber GmbH undertook the installation of two DN1500 liners using material provided by IMPREG. The liner selected had a wall thickness of 11.9 mm and the two liner runs were 161.9m and 75.1m long respectively.

A major challenge for completion of the liner operation was the weight of the liners being used, the largest being that for the 161.9 m run which was 17.8 t, the smaller liner being 8 t. Under the leadership of Wiener Linien, the first test section with a total renovation length of 237 m in the two sections, comprising 161.9 m and 75.1 m, was discussed with the relevant contact persons and the project managers of Swietelsky-Faber sewer renovation in the first quarter of 2023. Swietelsky-Faber Kanalsanierung also received technical support in the preparation and clarification of technical questions from the manufacturer of the liner, IMPREG GmbH. The intensive collaborative planning and preparation of the highly demanding project convinced Wiener Linien to award the renovation contract directly to Swietelsky-Faber Kanalsanierung. Not only was the special profile of the pipe challenging, but also the local conditions led to extensive preparatory work, such as the precise manual circumference measurement of the profile in a wastewater-free state.

In order to ensure the successful installation of the two liners, two DN1500 shafts had to be sunk in advance to a depth of 6 m. These shafts were absolutely necessary in order to be able to carry out the renovation work with the entire equipment and vehicle fleet outside the tram gauge to ensure maximum safety. Based on the circumference measurement and the static requirements, the old pipeline showed severe spalling, local breakouts and cracks. So, IMPREG GmbH produced two ‘custom-made’ liners with a total wall thickness of 11.9 mm each for the two installation sections. In order to ensure complete hardening of the liners or the laminate over the entire wall thickness, both liners were produced with peroxide to support the curing reaction.

For installation, the old sewer was cleaned using high-pressure jetting and the sliding film to assist the liner installation was installed. This protects the hose liner from mechanical damage whilst it is being pulled in. The most demanding part of the work began with the delivery of the liners. The liners were pulled in using a cable winch corresponding to the liner weight. In order not to exceed the maximum pull-in forces on the liners, both liners were pulled in using a conveyor belt with a folding device. After being pulled in, the liner was then closed on both sides with a packer and, in the next step, inflated using compressed air. In order to optimise the installation phases in terms of time, a second compressor was also used. After completing the installation process, the UV light source modified for this special profile was installed in the liner. The light source, from manufacturer Prokasro with 2 x 6 x 2,000 watts, was constructed with a special set of wheels in such a way that the irradiation of the laminate was carried out as centrally as possible, thereby ensuring complete hardening of the laminate over the entire circumference and over the entire wall thickness. By using the appropriate light source in combination with the optimal structure for the profile, a curing speed of 950 mm/min could be achieved. As part of quality assurance, additional temperature monitoring was implemented in both installations using sensors from Vortex. After the laminate had hardened and cooled, the light source and the packers were removed from the liner, the inner film was pulled out and the house connections were opened again manually. The final step was to dismantle the bypass wastewater system and put the combined sewer back into operation. With a staff of six very experienced and well-rehearsed employees, as well as collaborative planning and preparation by everyone involved, the complete renovation of the section with a length of 162 m was carried out in a time window of just 15 hours.