Redirecting wastewater flows with trenchless technology

Trenchless construction was recently completed at the Eaton to Bunbury Wastewater Pressure Main Project, south of Perth. Water Corporation oversaw the pipe installation, which now redirects wastewater flows from Eaton to the Bunbury Wastewater Treatment Plant in the Shire of Capel. Thanks to Australian made kwik-ZIP spacers used throughout the project, contractor DM Civil has been able to safely and efficiently carry out timely trenchless construction.

img_3902The pipeline project spans 18 kilometres between the pumping station on Monash Boulevard in Eaton, to the treatment plant in Bunbury, and will aid in ensuring that the long-term growth in the Shire of Dardanup is effectively serviced.

Eaton is located close to the border of Dardanup and the Shire of Harvey, and is one of the fastest growing towns within the region. With an annual population growth rate of 2.1 per cent according to the South West Development Commission, the importance of effective wastewater management remains clear; not to mention the overall south west region of WA anticipated to reach a population of 230,000 by 2026.

Project details

Prior to the new pipeline’s construction, approximately 3.5million litres of wastewater from both Eaton and Australind arrived at the Kemerton Wastewater Treatment Plant (KWWTP) located north of Bunbury each day.

The new pipeline now relieves the Eaton load from the Kemerton plant, and allows for effective treatment of wastewater throughout the Shire.

The long-term growth in Australind will continue to be serviced by the KWWTP.

Pipeline construction method

Open trench excavation, followed by backfill and restoration was the approved construction method for most of the pipeline route, however construction beneath all major roads and rail crossings, as well as the Preston River was completed with trenchless techniques.

DM Civil was contracted to complete trenchless construction at these sites, undertaking a total of sixteen trenchless crossings of varying soil conditions.  

Six of these crossings involved tunnelling beneath major roadways such as the South Western Hwy, Bunbury Bypass and Washington Avenue. The Preston River crossing involved a 310m drill shot with the DN450 HDPE pipe being directionally drilled direct using a Vermeer D100x120 HDD machine, with ground conditions alternating between sand and clay layers.  Two crossings took place beneath a major railway line.

DM Civil Manager, Scott Feilding commented on the diversity of the project.

“This was a considerable trenchless contract given the number of crossings involved and different methodologies to be used. This included slurry microtunnelling, thrust boring, guided auger boring and horizontal directional drilling.”


img_3909Using effective, high-quality and long lasting materials in any construction is key to the longevity of an installation, and during this project, DM Civil used Australian owned kwik-ZIP spacer systems throughout.  

Designed and developed by drilling professionals, the kwik-ZIP HDX range of spacers handle casing, bar and pipe diameters from 100mm OD to greater than 1600mm. Each spacer is manufactured Kwik-ZIP’s engineered thermoplastic blend – a high-grade thermoplastic that is flexible, extremely tough and has a low coefficient of friction, and high resistance to organic chemicals, oils and synthetic detergents; even when immersed for long periods of time.

Using a unique “load sharing runner” system, each HDX unit maximises its weight bearing capacity by distributing the pipe load across multiple runners. This reduces point loading at any one location, boosting and optimising the overall support capacity of the spacer exponentially as pipe size increases.

The “load sharing runner” system also delivers a suspension and dampening effect, resulting in a reduction in the transfer of potentially damaging vibration and movement from the outer casing to the carrier pipe.

This will be particularly beneficial to the project’s high traffic crossings where ongoing external vibration could affect the outer casing.

According to Mr. Feilding, kwik-ZIP spacers are cost effective, easy to use, resilient and flexible, and have so far been effective throughout installation.

“Due to our trenchless installation capabilities ranging in diameters from DN150 to DN1600 we particularly like the kwik-ZIP spacers given their flexibility to adapt to these diameters by simply adding additional segments.

“The fact that they are locally sourced is a great benefit when compared to the majority of the competitors spacers being sourced internationally,” said Mr Feilding.