Sunshine Coast Sewerage Upgrade

The communities of greater Caloundra on Queensland’s Sunshine Coast have experienced significant population growth with numbers expected to double by 2031, putting pressure on the region’s aging sewerage infrastructure.

The Challenge

Unitywater decided to invest over 30 million dollars to upgrade its sewerage network to meet the needs of the growing community while also alleviating the incidence and severity of overflows during extreme wet weather events. Trenchless specialist contractor Pipeline Drillers was selected to install a total of 5.7 kilometres of new pressurized HDPE PE100 sewer pipeline, of which 81% employs trenchless techniques to minimise impact to the community and environment.

How did Qenos help?

The pipe was manufactured by Vinidex in its Toowoomba extrusion plant. The up to 100 millimetre thick wall of the pipe meant that high melt strength Alkadyne® HDF145B had to be used. Combined with Vinidex’ unique know-how and state of the art extrusion line with melt cooling, the resin resists slumping and allows for the production of large bore pipes with tight control of dimensional tolerances.

Results

The longest bore

In Caloundra, the 2.5 kilometre long DN900 PN16 pipeline made from Qenos Alkadyne® HDF145B consisted of two bores including one of a record breaking 1600 metres, representing Australia’s longest horizontal directional drill of this pipe size. Piloting and reaming of the 1200 millimetre wide borehole using a 250 and 500 tonne maxi drill rig and a combination of rock reamers took seven months. Six pipe strings, each more than 250 metres in length were prepared prior to pull-through, and then welded together one to the next as the pipe was pulled through the borehole. Short trenching sections connect the new pipe to the existing sewer mains and pumping stations.

Increased safety factor for river crossings

The second pipeline section, located at Kawana Waters, is 3.2 kilometres long. It includes three bores, the longest being 1200 metres, and two others running beneath the Mooloolah River. A PN20 rated pipe with a higher wall thickness and an increased safety factor was selected for this challenging task. The robust pipe needed to resist high bending stress created by the tight curvature during pull-through while navigating in close proximity to residential properties.

After a year of drilling and pipeline works, including 4.5 kilometres of directional drilling, 1275 tonnes of PE resin, and 475 welds, the upgrade of the greater Caloundra sewerage network will be completed, achieving Australia’s largest HDPE pipeline installation by horizontal directional drilling.

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