Queensland Urban Utilities is investing AU$55 million to build a new 4.25 km sewer main between Wecker Road, Mansfield and Cadogan Street, Carindale in Brisbane’s southeast, known as the Bulimba Creek Sewer Upgrade Stage 2. Previous stages 1 and 1A of the project were completed between 2004 and 2013 in the suburbs of Mansfield, Wishart, Eight Mile Plains and Macgregor.
The existing Bulimba Creek trunk sewer services about 158,000 people to the southeast of the Brisbane CBD. It’s comprised of approximately 62 km of sewer pipes ranging in diameter from 375 mm to 1,650 mm and discharges to the Gibson Island Sewage Treatment Plant. Works are expected to be completed by the end of 2018, weather permitting.
“This project will cater for future growth and development in the catchment area for at least the next 50 years and reduce the likelihood of sewage overflows,” said Queensland Urban Utilities Principal Engineer Scott Stevens.
Queensland Urban Utilities developed a Reference Design and undertook all preliminary investigations along the selected route. All construction works were outsourced under a two-stage competitive open tender process and an Australian-Japanese joint venture (JV), comprising of Abergeldie Constructions Pty Ltd and Obayashi Corporation, was appointed to design and construct the upgrade.
“The Abergeldie-Obayashi JV was selected via a robust ‘value for money’ assessment that considered tunnelling experience, design and construction capability, capacity to deliver the work, proposed methodology, proposed tunnelling and other construction, plant and equipment offered to undertake the work, as well as delivery management, quality, safety and environmental standards.
“We thoroughly review the design deliverables to ensure it meets our quality and design standards before approving each stage. Queensland Urban Utilities also manages all community engagement activities.”
The project team is comprised of experts from across the utility, including principal civil, mechanical and electrical engineers, contract managers, health and safety officers and community engagement consultants. Multiple parts of Queensland Urban Utilities has an internal stake in the project, including infrastructure delivery, planning, the utility’s shareholder team, as well as media and marketing.
Brisbane City Council is an external stakeholder in the project, along with residents and businesses in the construction area and other users of the road, footpath, bikeway and recreation grounds.
A feasibility study identified several potential options for the sewer’s route, in length and construction techniques. However, the most direct and cost-effective path was along Scrub Road, using microtunnelling through Belmont Hills Bushland Reserve.
Speaking on the project, Abergeldie Complex Infrastructure’s Tunnels and Shafts Manager Grant Schultz said, “As it’s a gravity sewer, the depths required to maintain grade are up to 47 m below ground level, which eliminates a trenched option.
“In addition, the alignment travels along and across major roads with residential buildings on both sides of the road. Thus, the trenchless option allows for small work sites which minimise disruption to the community.”
Mr Stevens agreed that the depth ruled out open cut methods.
“Given the depth of the proposed sewer was more than 40 m, only modern trenchless methods proved feasible. The final alignment utilises long drives (several curved) and strategically located shafts to minimise disturbance to local residents and motorists,” said Mr Stevens.
“The tunnel drive lengths range from 550 m to 850 m. Several of the shafts have been designed to specifically launch in both directions to reduce the required sizes of the deep retrieval shafts.
“The deepest shaft being constructed is a 5.5 m diameter retrieval shaft approximately 47 m deep, near the top of Belmont Hill Bushland Reserve. The footprint of the physical works for the bulk of the tunnel construction is limited to a confined site located at strategic positions to avoid disruption to the community.”
The proposed length of the drives, depths and geologic conditions, meant that selection of the microtunnel boring machine (MTBM) was critical to the success of the project. Abergeldie decided on a Herrenknecht AVN1500TB, named Sewey, to complete the job.
“The AVN1500TB is a slurry shield MTBM. This type of machine is perfectly suited for excavating through the varying ground conditions that are expected to be encountered and the drive lengths that were required,” Mr Schultz said.
Expanding on this, Mr Stevens said “As sections of the tunnel alignment are 30 m below the water-table, it is imperative that access to the face can be achieved under all circumstances.
“As risk mitigation, the contractor opted for a machine capable of utilising a hyperbaric chamber (air lock), which would enable safe access to the face when required if groundwater inflow rates exceed the pumping capacity.
“The minimum recommended size machine to accommodate an air lock is 1,500 mm ID, which was an influencing factor in the selection of the Herrenknecht AVN1500TB machine. It utilises a medium voltage supply and in-machine power pack and permits drive lengths in excess of 850 m.
“The preferred jacking pipe material for the project was 1,780 mm OD, SN55,000 ‘Flowtite’ glass-reinforced plastic (GRP) jacking pipe supplied by RPC. The pipe was supplied in 6 m lengths which reduces the frequency of pipe changes, maximising production.
“The pipe joint permits enough deflection to safely navigate the desired 1,000 m curve drives without impacting the jacking capacity of the pipe. Given the long drive lengths and curved alignments, a VMT Navigation system in combination with frequent gyro surveys is being used to ensure the sewer is constructed within the desired horizontal tolerances and grades.
The next scheduled drive from MH5 to MH6 is 850 m in length and utilises a 1,000 m curve over the first 230 m, it will traverse through Argillite and Brisbane Tuff and beneath the Bulimba Creek with reduced cover (3.6 m).
“The drive, when completed, will be the longest pipe-jack using GRP pipe materials in Australia,” said Mr Stevens.
The project has not been without challenges, especially from a community engagement perspective as above ground construction work is very close to houses and includes round-the-clock tunnelling. Mr Stevens explained that the project management team has taken a number of measures to mitigate these impacts such as installing sound suppression barriers around the shaft sites, limiting truck movements during peak times and using approved traffic management to ensure the safety of motorists and pedestrians.
“Queensland Urban Utilities committed to a ‘no-surprises’ approach with all stakeholders, including the community, promising to be open and transparent about the works and how the impacts will be managed. Residents can also call the project team for assistance or information at any time on a dedicated hotline,” he said.
“One of the work sites is at the edge of a local rugby league football field and we need to use their car park for access. To minimise the impacts on the club, we reduced deliveries during game times, graded the car park surface regularly and also sprayed water to reduce dust.
“We also involved the local club in the project by facilitating a competition to name and design the MTBM. In addition, five sewer maintenance holes off Wecker Road have been transformed into colourful works of art.
“A local artist worked with students from a nearby high school to come up with designs. These creative initiatives were not only a way to ‘give back’ to the community, but we hope they have inspired local residents to think about their sewerage service. With most sewer pipes hidden underground, it’s easy for people to flush and forget.”
Preference for trenchless
Queensland Urban Utilities uses trenchless methods where possible, to reduce the impact on the community and increase safety for its workers. It is using no-dig methods for other projects underway at the moment, including microtunnelling a new service tunnel that runs beneath the Brisbane River from Kenmore to Jindalee in the city’s western suburbs.
“The service tunnel will accommodate new water and sewerage pressure pipelines. The tunnel is a 560 m curved alignment (compound vertical and horizontal) and traverses from alluvium and hard bedrock, below the water table,” said Mr Stevens.
“The tunnelling is also being undertaken by Abergeldie-Obayashi, using an AVN1500TB machine. The use of the hyperbaric chamber mounted on the back of the machine has proved crucial to the success of the project, providing safe access to the front of the machine to permit cutter changes and maintenance.
“Horizontal directional drilling (HDD) will be used for another cross river water pipeline from Murarrie to Pinkenba in Brisbane’s east which has been designed and constructed by Comdain Infrastructure.
“The new Bartley’s to Wellers Hill river crossing consists of 2 km of DN 750 MSCL trunk water main and a 800 mm OD, PE PN 20 HDD approximately 1.1 km in length beneath the Brisbane River. The drilling operations, which will be undertaken by Coe Drilling, will use bi-directional drilling techniques.”
As well as capital projects responding to growth, Queensland Urban Utilities also employs trenchless methods to rehabilitate aging assets, such as relining Brisbane’s largest and oldest sewer pipe, the S1 Sewer. It is also undertaking water main relining trials with the intention to utilise possible trenchless technologies to rehabilitate vast kilometres of AC and cast iron pipe within the reticulation network.
“Queensland Urban Utilities is committed to excellence in water and sewerage services that meet the evolving needs of our customers and enhance our communities,” said Mr Stevens.
This article was featured in the September edition of Trenchless Australasia. To view the magazine on your PC, Mac, tablet, or mobile device, click here.
For more information visit the Queensland Urban Utilities website.
If you have a project you would like featured in Trenchless Australasia contact Managing Editor Nick Lovering at nlovering@gs-press.com.au