640 metres in one go

The contractor Pfeiffer based in Kassel deployed a burstlining rig type RBS 1500 from Olpe-based ABS Trenchless on a spectacular job in Aalen. The state water supply agency of Baden-Württemberg had contracted Pfeiffer to remediate a 900 mm diameter drinking water pipe. The task was to renew the pipe to a maximum diameter without damaging, or indeed destroying, it.

The best solution was a swagelining technique whereby a PE pipe is drawn-in to close-fit inside the existing pipe. This is a key advantage, as the pipe is a supply line through which drinking water is pumped under high pressure. This eliminated the need for subsequent cost-intensive backfilling of the annulus between the old and new pipes to prevent the pressurized pipe from moving.

In simple terms, swagelining means that a PE pipe – in this case OD = 900 mm – is pulled through a kind of funnel, thereby reducing the diameter to 840 mm. The complete pipeline was pulled through the swagelining machine at a virtually constant force of 85 tonnes, with the lower outer diameter of 840 mm being retained for as long as the tensile loading is maintained on the pipeline.

When the complete length has been drawn in and the tensile loading has been reduced, the PE pipe attempts to return to its original 900 mm diameter. However, it can only do so until it reaches the inner diameter of the old pipe. This results in a positive-locking join between the old and new pipes.

It was necessary to draw in the complete length of 640 metres because the existing pipe runs beneath a housing estate. A number of houses, as well as trees, had to be bypassed in an arc. The arc was so tight that it could not be executed with a conventional system. This was where Pfeiffer's Rope Bursting System (RBS for short) came into its own, as such arcs pose no obstacle to its pull cable.

Since construction sites on this scale are not an everyday occurrence, the works were made public. The site owner allowed spectators on-site to view some of the interesting aspects of the project. It was an imposing sight: Two 900 mm diameter pipelines stretching a length of 320 metres were pre-welded and then drawn-in to the existing pipe. Including a four-hour break during which the two pipelines were welded together, the specified 640 metres were drawn-in in a single day.

After a long day's work, the representatives of the Baden-Württemberg state water supply agency and the specialists from contractor Pfeiffer all expressed their satisfaction. And the many interested spectators on-site also went home having seen something they would never forget.

ABS Trenchless GmbH
Oberveischeder Str. 5
D-57462 Olpe
Germany
Tel.: +49 2722 / 98 44 1-0
Fax: +49 2722 / 98 44 1-20
E-Mail: f.albrecht@abs-trenchless.com
Internet: http://www.abs-trenchless.com