Volcanic rock and a shared trench proved a dynamic challenge to the latest water and gas installations in the urban fringe town of Donnybrook in Victoria. Located within one of Australia’s fastest growing municipalities, the need for new infrastructure became paramount, with Yarra Valley Water, APA Group, Mirvac and Comdain Infrastructure stepping up to the challenge. AHD Trenchless was contracted to complete multiple trenchless sections within the project.
With the population of Melbourne set to become the largest in Australia by 2050, it’s no surprise that a consistent flow of home buyers are making their way to Melbourne’s outer suburbs. The City of Whittlesea, home to the rural towns of Merrifield and Donnybrook, is no exception, welcoming almost 8,000 new residents in 2014 alone.
Construction of the Donnybrook water and gas project, located north of Melbourne, began in mid-April 2015 in order to increase distribution to these areas in need. Water and gas pipelines were constructed along Donnybrook Road, and are currently servicing the Donnybrook and Merrifield precincts. Comdain Infrastructure was contracted by APA Group (on behalf of Australian Gas Networks) and Yarra Valley Water to complete the pipeline installations, which included utilising a shared trench for a section of the construction.
Installation of the gas pipeline
APA Group managed the construction of the gas main along Donnybrook Road for Australian Gas Networks (AGN). The gas main now forms part of AGN’s natural gas distribution network to the north of the Melbourne CBD.
The total length of the gas main is 10km and it is made from DN 300mm high pressure steel. 4.2km of the gas pipeline shares a common trench with Yarra Valley Water. According to APA, the ground conditions along Donnybrook Road posed a challenge for the workers on-site.
Ground conditions in the area comprised of clays and boulders from the underlying Quaternary Age Newer Volcanics basalt and there were multiple basalt flow boundaries along the alignment.
This meant that there was a lot of rock along the proposed trench alignment and heavy machinery was required to excavate the trench for water and gas.
The contractor elected to pre-break the rock with a rock breaker, followed by the use of an excavator to remove the rock from the trench. All trench material was then sorted and disposed of off-site.
Another challenge associated with the project was the alignment of forty-nine power poles located along Donnybrook Road that conflicted with the proposed location for the water and gas pipe.
In order to resolve future construction issues, AusNet Services and an accredited contractor were engaged to relocate the poles to a new alignment.
The gas main now delivers gas to new housing and industrial commercial developments in the Northern Growth Boundary that includes the Merrifield and Donnybrook precincts.
Installation of the water pipeline
The new water main is approximately 6km in length and DN450 in diameter. The diameter reduces in size to DN300 as it extends west to east along Donnybrook Road.
According to Pat McCafferty, Managing Director at Yarra Valley Water, “When installing the water pipe, traffic management along Donnybrook Road was challenging, given that it is a single carriage way road.
“We required the skills of a competent contractor with sound construction methodologies to maintain a functioning lane of traffic, while also providing the adequate room required to safely construct both mains in the road verge.
“We believe the solution reached in conjunction with VicRoads has minimised impact on the community as much as possible. This was particularly important when considering access to the Donnybrook township and residents along Donnybrook Road,” said Mr McCafferty.
Why a shared trench?
Construction via a shared trench method not only reduced the impact on the surrounding environment, but also provided customers with a clear point of contact for information on the works.
According to Mr McCafferty, “With a great deal of development occurring in the area, the shared trench method had the benefit of avoiding customers becoming frustrated or confused by receiving numerous communications from different organisations and potentially receiving inconsistent messages about work happening in the same area.
“This joint approach resulted in customers being engaged about several projects in the same communication, minimising confusion, and providing them with customer service expectations.
“Most importantly, customers were given one point of contact for information instead of several,” said
Mr McCafferty.
According to Ryan Buhagiar, Land Development Project Manager at YVW, the shared trench method was also beneficial in that it reduced the overall impact of the works on the environment as well as reducing community costs.
A shared trench was used to lay both water and gas pipelines simultaneously.
Working as a team
Installation of the twin pipes involved a lot of planning, preparation and collaboration between each of the contractors involved, said Mr Buhagiar, especially when construction took place beneath creek beds or railway lines.
“As a small number of contractors are accredited to complete both gas and water works, a significant amount of time was spent in researching the most appropriate procurement method to select the right contractor.
“As separate contracts are held for water and gas, this required a considerable amount of collaboration between APA and YVW to ensure the pipes could be installed safely. Both parties had to bring a degree of flexibility to the process to accommodate the respective governing technical requirements that each service was designed to.
“The major crossings of the Merri Creek, Kalkallo Creek, and railway also required careful consideration of the requirements imposed by the various authorities and stakeholders responsible for the respective areas,” said Mr Buhagiar.
APA agreed that the challenges of adopting a shared trench definitely involved the coordination of project activities and timelines to ensure the approach did not affect the delivery for the project for water and gas.
According to APA, while both parties managed their own processes for the planning and execution of the project, there was considerable amount of coordination of activities.
The approach also meant that both water and gas worked together to resolve issues identified with the alignment, said APA.
Trenchless construction
For construction beneath Merri Creek, AHD Trenchless was contracted to carry out trenchless Horizontal Directional Drilling (HDD).
The original 450mm steel open trenched water pipe was switched to a 560mm polyethylene pipe for the trenchless crossing, with the gas pipe remaining the same diameter throughout the project.
According to Anthony Doherty, Director at AHD Trenchless, the polyethylene pipe was chosen as it is more suited to trenchless methods, whereas policy surrounding the gas installation required consistency in pipe diameter across the total length of the pipeline. A Vermeer D100x120 and a Universal 220×350 drill was used by AHD Trenchless for HDD spanning a total distance of 150m beneath the creek, with a tight offset of 1.2m between the pipes.
“With a tight 1.2m offset between the pipes, accuracy and precision was top priority for our team throughout construction.
“The ground beneath the river was extremely hard and rocky, consisting mainly of volcanic basalt which required added time and care during drilling operations,” said Mr Doherty.
This was also a challenge for Drilling Superintendent, Gerard Hogan, who said that his team had to take extreme care when drilling the pilot hole, to ensure that the bend radius met the specifications of the gas pipe.
Benefits to the surrounding area
According to AGN, the new infrastructure will identify the future location of housing for the new town and neighbourhood centres and local employment areas, new social and community infrastructure, parks, open space networks and green corridors.
All of this will be supported by a network of major roads, public transport, footpaths and cycle networks. The delivery of natural gas infrastructure to these new communities provide homeowners with the option to connect to an energy source that could lower their running costs and improve energy efficiency, comfort and reliability for their home, says AGN.
About the Victorian State Government North Growth CORRIDOR Plan
The Victorian State Government North Growth Corridor Plan is one of Victoria’s high-level integrated land use and transport plans that provides a strategy for the development of Melbourne’s growth corridors over the coming decades.
The North Growth Corridor Plan projects a population of 60,000 established over six precincts associated with the Merrifield Development, which incorporates 37,000 residential lots.
Merrifield is located about 30km north of Melbourne’s city centre, on Donnybrook Road near Kalkallo.
The Merrifield Town Centre has been planned to support up to 160,000 square metres of retail space and a range of residential, commercial, civic and community uses.
About Australian Gas Networks (AGN)
Australian Gas Networks owns about 23,000 kilometres of natural gas distribution networks and 1,100 kilometres of transmission pipelines, serving over 1.2 million consumers in South Australia, Victoria, Queensland, New South Wales and the Northern Territory.
