Drinking water pipe rehabilitated trenchless

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In Bad Hall, one of the oldest drinking water pipes still in use has to be replaced. The old fibre cement pipeline in OD 250 mm has already been at its capacity limit for some time. In addition, some pipe bursts had to be repaired in the course of time. AGRU pipes with protective layer in OD 315 mm and SDR 17, which are installed using the burstlining method, are now being used as replacements. The soil-protecting rehabilitation method saves the disposal of the old pipeline and ensures the exact positioning of the new pipeline in the original pipeline route.

A 450 m long pressure line for the elevated tank Voglhub in OD 280 mm and a 1,800 m long transport line branching off from this elevated tank in OD 315 mm will be installed. On its way to the Pfaffenwimm elevated tank, the transport pipeline overcomes a height difference of 17 metres and the pressure in the piping system at the lowest point rises to 5.5 bar. “Unfortunately, there have been a few pipe bursts in this area in recent years”, says Anton Pöllabauer, Managing Director of the Bad Hall Water Association. As the maintainer of the new PE piping system, quality and service life are very important to him: “The last fibre cement pipe was installed in 1979. For more than 20 years we have only been installing PE piping systems from AGRU. We have rehabilitated older water pipes with AGRU PE 100-RC pipes using the burstlining and ploughing method and have had very good experience with this. We assume that the newly installed lines will have a service life of at least 50 years.”

In the target pit, the seg-ments of the drawbar are removed from the machine and stacked.

Lower installation costs thanks to long pipe strings

In order to ensure the most economical installation possible, the burstlining method is also used this time. Since the installation costs decrease with the length of the pipe strings to be drawn in, it is important to install only the maximum possible pipe lengths. The contractor, WDS Bau GmbH, an Upper Austrian civil engineering specialist known for the careful installation of pipelines, calculates the maximum draw-in lengths between the start and target pits on the basis of the soil conditions and the resulting tensile forces of up to 250 bar pressure. The up to 144 m long pipe strings are welded on site by butt welding from 18 m long protective layer pipes made by AGRU Kunststofftechnik GmbH. Sureline III pipes with protective layer offer double safety, as the stress crack-resistant PE 100-RC core pipe is protected from the shards of the burst pipe by a scratch-resistant protective layer made of PP when the pipe is drawn in. An additional advantage is the fast butt welding due to the factory stripped ends. AGRU Kunststofftechnik provided a CNC-controlled butt welding machine for the welding process. Thanks to the new technology, temperature, pressure and time are pre-programmed, thus ensuring the quality of the welds. The parameters of each individual weld and the name of the welder are also documented. The finished pipe strings are then drawn into the old pipe using burstlining. Burstlining is a cost-effective rehabilitation method for trenchless, underground renewal of pipelines made of brittle materials. By breaking up the old pipe, a new pipe with a considerably larger diameter can be drawn in. Some preliminary work is necessary for this purpose.

Burstlining – how it works

First, a camera is used to navigate the old pipeline. Fittings made of metal or cast concrete cannot be broken open and must therefore be removed using an open construction method. Then the start and finish pits are excavated at precisely specified intervals. In the starting pit there is the bursting head with expansion cone on which the pipe string to be drawn in is mounted. In the target pit there is a hydraulic traction device. The old pipe runs between the two pits, into which a drawbar consisting of numerous segments is inserted. The travel of the hydraulic cylinder of the towing device corresponds exactly to one segment of the drawbar.

The bursting head is now mounted at one end of the drawbar. The opposite side of the drawbar is attached to the towing equipment. By pulling the drawbar, the bursting head breaks the cement pipe into pieces. The following expansion cone displaces the resulting shards into the ground and makes room for the larger dimensioned new pipe that follows. In this way, the old pipe can be destroyed, the pipe channel widened and the new pipe inserted in one go. The construction site team in the target pit removes the new segment of the drawbar that arrives in the pit after each pulling operation. This process is repeated until the bursting head and the pipe behind it finally reach the target pit. The tensile forces acting on the pipe are electronically recorded and documented throughout the entire time. After successful installation, the complete piping system is disinfected and subjected to a pressure test.

Mr. Gerhard Dieringer is Managing Director of WDS Bau GmbH: “The welding machine provided by AGRU worked perfectly. We have divided the site into 12 sections for burstlining. Per day we were able to burst 1-2 sections and pipe them again. We were very satisfied with the products and services of AGRU Kunststofftechnik GmbH from preparation to delivery and quality”.

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