The street is a promenade, an intensively used shopping street and an important traffic artery. Frequent tramlines travel through the Ostertorsteinweg from the early morning into the night.

The mixed water conduit, up to 6 metres below, is as important as the street itself. Over 104 years of operation has left its mark on the brick oval profile 800/1200. Above all, the advanced level of corrosion of the brick joints made the sewer a rehabilitation project, according to the technical assessment of HanseWasser (Hamburg Water Works). The goal was a long-term preservation of the structure.

Tight timing

The concrete project planning was triggered by a rehabilitation project on the street surface. As the tram rail track of the Ostertorsteinweg was up for renewal, the opportunity was taken to repair the underground assets. The track renewal determined the timing of the sewer rehabilitation, which would take place in three construction sections, according to the planning of HanseWasser. While the second and third construction section between Poststraße, Mozartstraße and Goetheplatz would be undertaken when the tram traffic had already been suspended.

The construction of section one between Bauernstraße and Poststraße was set for roughly one month earlier and had to be coordinated with the running tram (ÖPNV) operation. This resulted in an extremely tight time schedule. To avoid impeding the rail traffic, the maximum time frame was from Friday 9:00 pm (last tram) to Monday 3:00 am (first tram). In this corridor, two liners of 32.5 metres and 173.6 metres in length had to be installed, including all preparatory and related work.

Light-curing GFRP liner

The related work included the opening of the connection lines that are covered up by the liner. This work played a decisive role in the selection of the process — due to the time factor. The planners at HanseWasser decided at the outset that only light-curing GFRP liner systems were to be considered. With this pipe lining variant there is no need to consider the reduction of stresses in the liner, which can take several days. The lack of shrinkage means that there are no axial movements and the connections can be milled out directly after the curing of the liner without the risk of changes in length.

Considering the high density of connections in Ostertorsteinweg and the fact that behind almost every connection there is a multi-storey residential building with retail space at ground floor level, smooth maintenance of the drainage was especially important. In order to maintain the drainage during the rehabilitation, DN 400 free-flow pipelines were installed above ground for temporary water drainage, including sufficiently powerful pumps.

At exactly 9:00 pm, the last train had just disappeared around the corner and the preparatory cleaning work began in the collection drain so that at 11:00 pm the Brandenburger construction crew could begin with the insertion of the liner through the start shaft near Poststraße. The 10.4 tonne glass fibre tube was let down into the opened shaft out of the transport packaging and, using an electrical conveyor belt, pulled with a steel cable connection to the target shaft at the Weberstraße. A foil that had been laid down protected it from damage. At 2:00 am on Saturday morning, the entire 173 metre length of liner lay in the Ostertorsteinweg collection drain. At the start and end of the shaft the liner was equipped with pressure locks so that it could then be expanded in the sewer using compressed air.

Lamp train and curing A lamp train with nine UV modules, each 1,000 watt maximum power, was pulled through the form-fit calibrated liner with pre-calculated speed. The connection to the new UV technology with the special resin recipe made it possible to also achieve curing in a very short time. The light-curing process lasted a total of four and a half hours at a train speed of 65 cm per minute and was recorded in all relevant parameters, including speed, exposure dose and liner temperature. The computer-aided documentation of this data allowed for any eventual deviations from target values of the technical parameters to be recognised immediately and allowed tracking of the curing procedure. Connection lines

Directly after the curing of the liner, work began to open the connections. By midday Saturday, all 48 residential connections in the rehabilitated collection drain were milled open and at the start of the tram traffic on Monday morning at 9:00 am they were all connected according to the specifications of the client. This was accomplished with the installation of glass fibre short liners up to 50 cm over the first pipe connection. The direct support area was filled with an epoxy resin system so that it was waterproof and had no cavities. The local residents were hardly affected by the project in terms of disruptive effects normally associated with construction projects.

Further construction sections

The combined second and third construction sections in Ostertorsteinweg were performed over ten days. As the tram traffic was already suspended, there was not the same degree of time pressure as in the first section. Two 115 and 128 metre long liners were installed with all preparatory and related work. There was a work pause of almost four weeks after the first construction section due to a large number of residential connections, in the area of the collection drain yet to be rehabilitated, that were renewed in open cut. This entailed excavation work but also the renewed preparation of the surrounding drainage conduit. The independent laboratory inspection, as a major component of the quality management system, was performed in the Ostertorsteinweg project by engineering company Siebert in Oststeinbek. Their analysis of the liner samples taken from the construction site came to the positive result that all specified parameter nominal values of all liners were exceeded by at least ten per cent. Summary

HanseWasser was pleased with the successful and on schedule completion of the rehabilitation project. The successful Ostertorsteinweg rehabilitation project accentuated not only the special advantages of the liner process that was used, but is also another example for the plus factors of the trenchless pipe lining technology as a whole.