Many trenchless projects will present unique challenges and obstacles, especially in busy and expanding urban environments such as the Gold Coast.
The Gold Coast, Queensland, offers a wide-ranging appeal to locals and tourists alike, demonstrated through its influx of visitors all year round and steadily increasing local population. Recognising this growth, the City of Gold Coast has taken a proactive approach in upgrading its civil infrastructure to ensure the city remains both liveable and a popular tourist destination.
Isle of Capri Bridge Project
The Isle of Capri Bridge Project is indicative of this desire, comprising the construction of a new four-lane bridge, along with road and intersection upgrades and the relocation of underground services including the sewer rising mains.
Serving as a major connection between the east and west areas of the coast, the project aims to minimise congestion and increase network capacity while avoiding disruption to more than 18,000 vehicles and users traversing the area daily.
As a vital aspect of the project, Pipeline Drillers Group was engaged by the City of Gold Coast to construct the sewer rising mains aspect of the project utilising trenchless methodology, including more than 500 m of horizontal directional drilling (HDD) of high-density polyethylene sewer lines and crossing the Nerang River.
The use of HDD allowed the project’s proponents to avoid short-term options like attaching services to the old bridge, and the limited capacity and life that these types of solutions present.
A challenging task
Pipeline Drillers Group Director John Whitbread says the challenges of the project were evident from the very start.
“If the Gold Coast looks busy on the surface, the same can be said for underground,” he says.
“We had our work cut out for us, with the large quantity and density of existing services; very small entry and exit work areas adjacent to the Gold Coast Highway, combined with the need for a maxi size HDD rig; and the need to maintain suitable depth of cover under the Nerang River and near the neighbouring tidal wall. And we needed to do this while minimising disruption to users of the area, as well as locals neighbouring the construction sites, all in dense sand conditions.”
However, there were significant advantages throughout the project as well, with Mr Whitbread saying the City of Gold Coast – as the client – demonstrated it had a great understanding of the project constraints as well as a creative and innovative attitude.
“This provided the perfect platform to work together really effectively, incorporating constraints and minimising risk, while coming to a really clever, modern HDD solution,” he says.
“We still knew that with the right design, risk mitigation, and correct tooling and equipment, the job was achievable.”
Conventional is not the key
Due to the existing services, obstacles and space constraints under the waterway, a conventional HDD design was not feasible.
“Knowing this from the start, we engaged our preferred HDD designer, Future-Proof Solutions, to review and improve the client’s design undertaken by SMEC. Together we were able to plan and conceive an innovative solution,” says Mr Whitbread.
The first issue faced was the limited depth of cover at entry, where a hydrofracture analysis showed the initially designed profile area was a high risk for drilling fluid release and bore hole collapse.
Mr Whitbread says to mitigate drilling construction risks, a hammering technique was used to install the sacrificial conductor pipe that minimised the disturbance to the sand conditions and stabilised the surface area of the bore hole prior to the commencement of HDD operations.
The next major hurdle was the excess of the existing services – including other HDD crossings – in the section under the river.
“We had to avoid the services, but we couldn’t risk introducing a compound curve, with their potential for doglegs, tooling snap-off and other HDD nightmares,” says Mr Whitbread.
“So, we worked with Future-Proof Solutions to conceive an innovative solution incorporating a combined radius for the section under the Nerang River, with the profile curving horizontally and vertically in the same section, with the same tangent points.
“With the modified design, and our construction experience and expertise, we were able to drill a much more consistent profile, steer pattern and borehole, with limited directional changes and the problems they introduce.”
However, the challenges continued once the profile had crossed the waterway, as the project partners still needed to target a suitable exit location while avoiding more existing services. To do so, a horizontal radius was incorporated into the 12° exit section, allowing a successful execution of this section of the hole and a punch out in the tight exit area as had been planned.
A community collaboration
Mr Whitbread says the project was supported by both internal cooperation and the wider Gold Coast community.
“The City of Gold Coast construction teams were sensible and committed to good outcomes for their communities,” he says.
“Their commitment to community engagement was sincere, and due to these efforts, the community was understanding and supportive of what we needed to do during HDD.”
Throughout the HDD project, the Pipeline Drillers Group team provided construction advice to guide the City of Gold Coast to a positive outcome.
“We delivered the project on time and on budget, allowing the larger Isle of Capri Bridge Project to progress without impact. It was a phenomenal success, especially considering the difficulties we had to overcome,” says Mr Whitbread.
“This project had so much going on that we really had to be creative. But this was only possible with the trust and collaboration of the City of Gold Coast. They let us do our job, thinking outside the box, and without that cooperation and innovative attitude from both contractor and client, there’s no way we could have achieved the great outcome that we did.”
This article was featured in the September 2020 edition of Trenchless Australasia. To view the magazine on your PC, Mac, tablet or mobile device, click here.
For more information visit the Pipeline Drillers Group website.
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