What is believed to be one of Australia’s longest 1 m diameter horizontal directional drilling (HDD) installations has been executed in Cairns, Queensland. With the worksite bordering a popular recreation facility and main road, the team used trenchless methods to complete work on the restricted site footprint.
by John Thompson, Senior Engineer Projects, Cairns Regional Council
Cairns is a tropical city located on a northern coastal strip in Queensland on the edge of the Coral Sea, near the Great Barrier Reef. It’s a popular tourist destination that attracts over 2 million tourists each year, with over 160,000 people living in the region residentially.
Cairns Regional Council (CRC) successfully completed a major sewer pipeline augmentation using various Trenchless Technology. It engaged local contractor JPMI, who in turn called in Pipeline Drillers and Bothar Boring & Tunnelling as sub-contractors, to install 465 m of large diameter sewer pipes which ran parallel to one of Cairns’ key sporting precincts.
The AU$3.23 million (US$2.4 million) project used horizontal directional drilling (HDD) for the installation, which is believed to be one of Australia’s longest 1 m diameter drills. The sewer upgrade caused minimal disruption to scheduled events at the popular recreation ground, including the opening of the AU$23.7 million (US$17.6 million) Tobruk Memorial Pool Redevelopment.
A network of sewer pump stations within the Cairns CBD feed into Sewage Pump Station K, before transferring the effluent via a 4.3 km rising main to the Marlin Coast Waste Water Treatment Plant. The rising main has the capacity to transfer over 600 L/s and was constructed in 1970 with diameters varying from DN660 to DN1000.
Over the last 45 years sections of the main have been progressively replaced. Age related operational issues emerged recently leading CRC to embark on the AU$3.25 million (US$2.41 million) project to replace 465 m of the main.
The section of the main where the work was focused ran parallel to the city’s key sporting precinct, which housed the Cairns Tennis Centre, Tobruk Memorial Pool, the Cairns Hockey Association, and a number of heritage listed buildings. The recreational facilities are home to several major sporting events in Cairns, from the local Ironman series to Masters Tennis tournaments and many more.
Dispersed through the sporting precinct are a number of significant trees, which add to Cairns’ tropical ambience and play an important role providing shade to spectators and passersby. As with many sporting precincts in the region, it was located in low laying reclaimed swamp land, with marine mud and sands below the surface.
Captain Cook Highway, a vital 75 km scenic road providing access from Cairns to the northern beaches, runs parallel to the pipe route and the recreational facility. The highway runs above several underground services and has future corridor requirements set by the Department of Transport and Main Roads that cannot accommodate the alignment of a trunk rising main.
Realigning the pipeline along an adjacent street was investigated during the planning and design phase, but was discounted due to the longer route, high cost of installation, loss of operations and high maintenance costs.
CRC liaised with land owners along the proposed route, agreeing that the final route should follow the existing rising main, along the eastern side of the highway. This avoided existing services and heritage listed buildings within the Tobruk Pool precinct, and preserved the large trees, which was a key consideration in selecting the construction method.
The restraints imposed by the sporting precinct, the highway and natural surroundings, resulted in the project’s tenders specifying the installation use a combination of trenchless pipe jacking and HDD, as well as a small amount of open trench work. The project works included: 35 m of DN1219 MS sleeve pipe jacking; 340 m of DN1000 PE100 HDD; and 90 m DN813 MSCL open trenching.
An entry pit was excavated near the corner of Captain Cook Hwy and Lily St, while the exit pit was to the north near the corner of the highway and Rutherford Street. The pipe was strung along Lake Street, on the eastern side of the recreational area, around the corner onto Lily Street before turning to be parallel with the highway and in line with the entry pit.
At a depth of 15.8 m, the installation avoided existing underground services. The 340 m installation of DN1000 HDPE, including pipe stringing and testing, was completed in 29 days. The challenging bore excavated through marine mud and sand, with less than 500 mm horizontal deviation from the designed exit alignment.
An agreement was reached to place the jacking pits on private land, within the easement. Jacking the 35 m of DN1219 MS sleeve under Rutherford St was therefore completed with minimal impact on road corridor users, as all associated jacking and receiving activities were outside of the road reserve.
The HDD installation achieved outcomes not possible with other methods. It was installed with minimal, to no, disruption to the tennis centre, hockey fields or Tobruk Memorial Pool, which were all hosting major events during the construction period.
No significant trees were damaged or removed, and it resulted in limited disruption to the environment. It also provided sufficient flexibility to avoid alignment under the heritage listed buildings, and required minimal dewatering compared to other installation methods. CRC Principal Engineer Peter Thoren said that teamwork played a vital role on the project, adding that the construction team went above and beyond the call of duty to complete
“To deliver complex projects successfully, the importance of teamwork can never be underestimated. I wish to acknowledge the contributions made by local contractor, JPMI Pty Ltd and their sub-contractors Pipeline Drillers, Bothar Boring & Tunnelling and others.
“Equally the efforts of Cairns Regional Council’s operational teams and inspectors should be acknowledged; working midnight hours to manage pump station flows and to assist with the connection works and the commissioning of the new main. Records show that 1 million litres of sewage were moved via vacuum trucks during the connection process, a phenomenal effort.”
Trenchless in Cairns
CRC has an AU$30-40 million (US$22.3-29.7 million) annual Capital Works Budget for water and waste related projects. The award of the AU$6.6 million (US$4.91 million) Rising Main T1 Upgrade and the AU$2.8 million (US$2.08 million) Shale Street Trunk Water Main, which both utilise various trenchless construction techniques, will be announced soon.
Trenchless Technology will also feature on future projects such as the Mt Peter Sewer Main and the Northern Beaches Bulk Water Supply Main Augmentation. Mt Peter will provide challenging construction conditions to construct a gravity main in built up residential areas, where the Northern Beaches trunk water main incorporates several highway and waterway crossings.
This article was featured in the Summer edition of Trenchless International. To view the magazine on your PC, Mac, tablet, or mobile device, click here.
For more information visit the Cairns Queensland website.
If you have a project you would like featured in Trenchless International contact Assistant Editor Nick Lovering at firstname.lastname@example.org