Due to the sandy soil and high water table of the area, it was decided that an open trench might be prone to collapse and pipe bursting would be the preferred replacement method. The ground conditions proved to be a benefit for pipe bursting, as they were less conducive to ground heaving and no heaving of the ground or streets were observed.
Pipe bursting brief
The chief advantage of pipe bursting versus open cut methods is that contractors can replace pipeline without digging up the old main. When using this system, the contractor excavates a launch and burst pit. A pipe bursting machine is positioned in the burst pit and steel rods are pushed out from the machine through the existing asbestos pipe to a launch pit.
Once the rod payout is complete, a conical tool/bursting head, which is 20 to 29 per cent larger than the outside diameter of the pipe being installed, is attached to the rod.
Article continues below…The pipe is then attached to the bursting head. Once the connections are made, the bursting machine begins to pull the rods back through the old pipe. The old pipe is fractured or split into small pieces, and pushed out into the surrounding soil as the new pipe is simultaneously installed.
The technologies used
The HammerHead HydroBurst® HB80 bursting system was used with 72.5 tonnes of static pullback force. The HB80 features an automatic rod spinner, 16 second payout per 90 cm rod, and storage capacity for 45 m of lightweight rod. Despite its capacity the HB80 weighs only 1,270 kg and is readily handled by a small vehicle loading crane on a support truck.
The HB80 burst an average of 40 m of pipe per day, including backfilling of pits and reinstatement of the service lines. On some days, the crew pulled in as much as 100 m of pipe. Overall, the project took 18 working days to complete.
A number of technologies were used to minimise service disruption to local businesses. The patented line stopping system isolates water mains under pressure, reducing the length of the bypass and avoiding the need to drain the mains and undertake planned shutoffs. It has been a major contributor to reducing the incidence of loss of water service during renewal projects, and over 95 per cent of these can now be completed without interruption to supply.
Complementing this system is a thermal control valve that mixes water heated by sitting in bypass lines with cooler water to provide water to the consumer at a comfortable, controlled temperature.
