Pipeline installations in developed areas are becoming more commonplace as populations grow. Unitywater, which provides essential services to the Moreton Bay, Noosa and Sunshine Coast regions of South East Queensland, was faced with this challenge when urgent work was required on a severely degraded sewer rising main at Fishermans Road in Maroochydore.
The project was further complicated by the popular Sunday market, bustling sports precinct and the need to replace and realign the major sewer rising main installed in 1977.
Unitywater Executive Manager for Sustainable Infrastructure Solutions Amanda Creevey says works were fast-tracked to reduce the impact on local business and recreators that access the Maroochy River.
“The completion of this project ensures we can provide reliable sewage services to around 10,000 customers and many more into the future, while also improving the efficiency of our network more broadly,” she says.
“By accelerating these works, the pipeline could also be brought online prior to the 2021-2022 wet season, when demand is at its peak.”
Unitywater contractor Pipeline Drillers Group helped make it possible with a horizontal direction drilling (HDD) project designed and delivered without delay.
Director John Whitbread says HDD was the natural choice to install approximately 550 m of new pipework by drilling 20 m underground to minimise disruption to the community and safeguard the new asset.
“We had the Maroochydore Multi Sports Complex, busy Fishermans Road, additional under and above ground services, and residential areas near the pipeline, so a trenchless option was a must,” says Mr Whitbread.
“With those factors, along with the pressing need to complete the project on a tight turnaround, we had for-construction HDD designs completed within a week of contract award. We knew the significance of this project and the importance of getting the HDD works done to allow for completion of the tie-ins and other larger project works, so timing was vital.”
As well as being time-sensitive, several other project-specific factors added to the complexity of the project, explains Pipeline Drillers Group Business Development Manager Paul Tredenick.
“We had building infrastructure and lighting services right in the middle of the alignment,” says Mr Tredenick.
“Additionally, ground conditions were challenging – penetration boreholes and diffraction surveys were taken in the project area, and they were demonstrating variable results. One area would show rock conditions at particular depths, while not far away, we’d get results of very low-strength, other-than-rock geology.”
Pipeline Drillers Group tackled these complexities with a risk-based approach.
“We minimised settlement, vibration, and construction risk to existing infrastructure by incorporating a significant horizontal radius into the design,” explains Mr Tredenick.
“And given the uncertainty in ground conditions, we included risk mitigation measures such as adding exit side casing into the design, and a set of lightweight tooling as well as rock tooling. With this approach, we could minimise risk of hydrofracture at shallow depths, but at the same time, we knew we could confidently handle any harder geology we might encounter.”
Pipeline Drillers Group mobilised its Herrenknecht 250T rig, along with a variety of auxiliary and standby equipment, to ensure minimal downtime during the seven-day schedule. Supported by classic Sunshine Coast weather, the 550 m, 450 mm HDPE crossing was completed ahead of schedule, within four weeks of project commencement.
Ms Creevey says that the project was a testament to the benefits of trenchless methods.
“By using HDD to replace and realign the Fishermans Road Sewer Pipeline, we were able to bring this important piece of infrastructure online quickly and efficiently, with minimal closures and disruption to our residents and local community,” she says.
For more information visit the Pipeline Drillers Group website.