Our alternative options provide the best solution for Roleystone DN760 Water Main Replacement.

September 2017

Perth Region Alliance (PRA) released a design and construct package to replace a section of the existing DN760 locking bar pipe over 150 metres. The section is located on a hillside leading off Butcher Road, Roleystone and down to the Canning River.

The submissions required two options to be offered for construction. The first option was to slip-line the existing steel pipe with a polyethylene sleeve and join back into the existing main with a butt welded PE flange and backing ring fixed to a steel flange with tapers to match the existing.

The second option was to remove the existing section of locking bar pipe and replace the length with DN630 PE and, as with the first option, join back into the existing main with a butt welded PE flange and backing ring fixed to a steel flange with tapers to match the existing.

DM Civil offered an additional third option to replace the length of failed pipe with new MSCL ‘Sintakote’ pipe. This would normally be a cost prohibitive option. However, our pipe supplier, Steel Mains, assisted us with competitive pricing to provide the best solution for replacement on a slope of 1 in 3 in a bushfire prone environment.

The client immediately chose the slightly more expensive, best engineering option and, following post-tender clarifications, awarded the contract to DM Civil.

There are tight timeframes and compliance requirements for all stakeholders involved. The terrain requires particular attention for safe construction. With a 1 in 3 slope, only tracked machines can be used.  Even walking up and down the pipe route is a physical effort.

Our experienced and skilled machinery operators will need to maintain vigilance on such steep slopes. Further operating restrictions include the neighbouring property to the East, which must be left undisturbed, and the existing live DN1370 pipe to the West, which must be protected from damage at all costs, as it is a vital water supply.

Our team is working closely with PRA to ensure that the project can be delivered safely and in a timely manner to meet the shutdown schedule for the adjacent DN1370 main. We await the final design document by our design partner, Wood & Grieve Engineers. These must then be approved by Water Corporation before being issued for construction.

The locking bar pipe, circa 1920’s, was the original feed line from Canning Dam. It has done a good job over the past ninety-plus years, taking into consideration the technology available at the time for both manufacturing and construction techniques.

The existing above ground pipe will be replaced with buried pipe covered by rock scour protection to prevent unearthing the pipe and to avoid cover material being introduced into the Canning River.

An existing scour point used for riparian flow to the Canning River in summer will be repositioned to a safer operating point. 200 metres to the North, a further task is to replace the existing DN600 gate valve with an equivalent butterfly valve with bypass arrangement.

This will be a fully spooled assembly dropped in as one piece and welded in place with flat and convex weld bands. The joints at either end of both locations will require special attention during welding.

We continue to demonstrate our diversity, motivation and commitment to ‘getting the job done’ under any conditions and provide tailored sustainable pipeline solutions.