Is it possible to carry out CIPP lining by means of the No-Dig method in a 400 m long sewer pipe – with a cross-sectional area of 2 m? When the liner alone weighs 140 tonnes and the pipe system is not suitable for lining?

Yes, it is possible, and the method is also cost-efficient. This was the good news from Århus Vand A/S in Denmark. In mid-March 2010, following nine weeks work, Århus Vand A/S could, in co-operation with the Danish engineering contractor Per Aarsleff A/S, admit water back into the 400 m long sewer pipe after a well-executed renewal. The sewer pipe was situated below a large sports centre and the lining operation was completed without disturbing one blade of grass on the playing fields.

Project background

The playing fields at Viby Stadium in Aarhus have been severely plagued by rats running freely both above and below ground. The rats have gnawed their way through the existing sewer pipe and all the way up to the playing fields, and in some places, the fields have been undermined by the rats’ activities. The legislation governing such matters is clear – the sewer pipe had to be renewed. The pipeline runs beneath two playing fields, an athletics field and the sports centre buildings. The project is the biggest CIPP lining project so far in Aarhus. Århus Vand A/S and Aarsleff have, in co-operation, found a new and unconventional way for this lining project to be completed within the old sewer system while accounting for the difficult circumstances.

The pipe system is a difficult cross sectional shape and not particularly suitable for CIPP lining. CCTV inspection clearly revealed that conditions were excellent for rats due to the existing flat benches in the geometry of the pipe. So the geometry of the old sewer pipe had to be converted. However, the football fields in Aarhus are very precious and a section of the pipe is, as mentioned, situated below a sports centre. Therefore, the solution was No-Dig to avoid excavation in the fields and the large cost of diverting the pipe away from beneath the buildings.

To complete the project, the companies had to think unconventionally.

Sophisticated technology

The cross-sectional shape of the pipe was quite unusual and had been cast in-situ in the 1950s. This added to the challenge of renewing the pipe. The advantages of applying a liner in pipes attacked by rats is that the rats rarely attack this type of renewal and that the liner has no joints. From a capacity perspective, the repair team could not allow large reductions of the cross-sectional area, as the capacity of the pipe had to be maintained.

One of the disadvantages was the specific cross-sectional shape. Therefore, the benches were cut off to convert the geometry of the old sewer pipe to best effect. New, rounded benches were cast, so that the pipe cross section now looks more like a v-shaped pipe but still with a flat cover. The static dimensioning of the liner was a challenge due to the geometry of the pipe. A model showed that restraints were required in the top of the pipe. This was solved by installing a corrosion-resistant steel profile.

Successful partnering co-operation

In the partnering co-operation between Århus Vand A/S and Per Aarsleff A/S both parties contributed a choice of solutions and decisions at a very early stage. Everybody focused on quality and costs and consequently everyone felt that they had ownership of the project. This meant that the project costs were sustainable and the outcome was successful. The people at and around the stadium can now look forward to a new season where the turf is unaffected by the major renewal project – and without rats as spectators.

In partnership, the team managed to find a method to avoid bypass pumping. This was achieved by sealing off the pipe and letting the water run backwards in the system and through a major collector pipeline to a nearby treatment plant. In regard to occupational health and safety, the project was also a success. We held regular safety meetings where everyone involved participated and where many constructive proposals were presented. For example, we put up CCTV in the pipeline during the conversion of the benches, we put up fixed lighting for eight weeks and we carried out a safety drill (evacuation drill).

Overall there was a feeling of satisfaction from the project managers in a company that has an occupational health and safety certificate.