The company was recently engaged to construct a new pipeline which included the delivery of an HDD crossing of the Shoalhaven River in New South Wales.
Local utility Shoalhaven Water maintains the clean, regular and efficient water supply of 96,000 people and is implementing its Reclaimed Water Management Scheme (REMS) to collect and store reclaimed water and apply it to agricultural land and sports grounds in the region.
First commissioned in 2002, the scheme now includes 14 dairy farms, 2 golf courses and several sporting grounds with reclaimed water for irrigation to well more than 6 km2 of land.
The second stage of REMS involved major upgrades to the Bomaderry and Nowra wastewater treatment plants to increase both the capacity and level of treatment at each site, and achieve a high quality of reclaimed water for use.
Contracted by UGL for Shoalhaven Water, UEA’s works were to include a 2.9 km transfer main to allow reclaimed water to be conveyed between the two treatment plants for final disinfection and be transported into the existing REMS distribution systems.
Planning stages
UEA’s engagement on the project included the construction and commissioning of the proposed pipeline connecting the Bomaderry and Nowra facilities.
The Bomaderry to Nowra transfer pipeline had several significant hurdles to overcome before being approved for construction.
UEA’s scope of work included the development of the overall pipeline, taking the plans through to design based on further geotechnical data, consultation with stakeholders, review of suitable pipeline materials, performance criteria and construction methods.
This collaborative process was undertaken over an extended period of time, allowing input from the client, contractors, operators and impacted stakeholders.
Responsible for the end-to-end construction of the nearly 3 km pipeline, UEA set to establish site compounds, one with an engineered sound wall, and commence construction on numerous fronts to condense the already ambitious works program.
The critical path of the project had always been the major horizontal directional drilling (HDD) crossing of the Shoalhaven River being 1,410 m in length and the expectation a mixed bag of ground conditions including sand, silt, clay, gravel, cobble and hard metamorphic rock.
To help manage the unstable and problematic overlying ground conditions, steel conductor casing was required to be seated fully into rock from the entry side to not only prevent intrusion of overlying soils but escape of drilling fluids to the sensitive marine environment.
Shoalhaven Water Executive Manager Robert Horner said UEA’s part in the project was integral to its success.
“Being a river crossing, the pipeline traversed to approximately 30 m below the bed of the Shoalhaven River at its deepest point, so getting accurate geotechnical information was a real challenge,” he said.
“UEA’s component of the project was design and construct. We gave them some basic geotechnical information, but it was basically up to them to complete the detailed design.
“Nobody was 100 per cent sure that the crossing and the drilling could be achieved until we had the detailed design information. We worked very cooperatively with UEA.”
Boots on the ground
Additional geotechnical boreholes undertaken during the design phase had shown loose soils, gravel and cobble present and had informed a casing length of up to 130 m – a length never undertaken by UEA previously.
Casing installation was successfully completed to 129 m from the rig using a variety of methods and casing sizes.
Commencement of the pilot bore, the guided portion of the HDD works, started as planned and proceeded well until approximately 550 m out from the drill rig.
Historical geotechnical borehole logs and seismic data had inferred that the rock profile was horizontally planed, but during the pilot hole construction an ancient paleo channel was encountered resulting in potential fluid loss given the extended length of the bore.
Works onsite ceased while calculations to allow the pipeline to be installed deeper were confirmed.
Upon design confirmation the pilot bore was recommenced at a level 10 m lower than the previous design and successfully completed in rock across the Shoalhaven River, under the Manildra Group Ethanol distillery plant to the designated exit point without fluid loss to the formation.
A second Maxi rig was mobilised to the northern side of the river to undertake the 24 inch (610 mm) back ream for the 400 mm PN32 HDPE pipe. Back reaming commenced shortly after mobilisation of the second rig with the aid of a tailstring to help secure the borehole at all times.
Punishing conditions caused significant wear on the HDD tooling and resulted in slower than expected progression, although the overall works program was still able to be maintained.
Correlation between later geotechnical boreholes, progression rates and tooling wear confirmed rock strengths more than 250 mPa for the deeper sections of the bore – some of the hardest rock UEA has ever had to drill.
With the completion of the pilot bore and reaming underway, attention turned to the other required works – three minor HDDs from 36 to 200 m in length, more than 1 km of trenching in potential and actual acid sulphate soils and the installation of associated valves, pits and fittings.
The open cut trenching progressed well on three fronts and allowed all minor HDDs to be tied into the overall pipeline works.
Also undertaken during for major HDD reaming operation was the welding, stringing and testing of the unique and Australian first 400 mm PN32 HDPE pipe.
Manufactured by Vinidex under strict quality control standards witnessed by UEA as part of the project QA system, the 400 mm PN32 pipe made to European Standards out of H112PC resin otherwise known as PE112, allowed for a lower slump, more uniform wall thickness and stiffer pipeline.
For added security and lower risk, an above ground pressure test was undertaken to ensure compliance with the specification as well as a rigorous 1:10 destructive weld test frequency passing all required NATA tests.
Although slower than anticipated, the back reaming was completed in one pass using multiple reamers to achieve the final reamed borehole.
At the completion of the reaming pass, a suitable sized barrel reamer was used to pig and prove the borehole ready for pipe installation.
Although reamed by the drill rig on the northern side of the bore, given the available pipe welding and stringing room the pipe was installed by a rig based on the southern side of the river.
Shoalhaven Water Executive Manager Robert Horner said being able to deliver this HDD crossing was vital to the efficiency, time and cost parameters of the project.
“If we couldn’t achieve the pipeline crossing, then we would have to have diverted or constructed a pipeline through basically the town centre of Bomaderry and then to the Shoalhaven River bridge, traversing through rock, and crossing across the bridge and then to the Nowra treatment plant,” he said.
“We would probably still be designing that now if the drilling had failed. It was an extremely important part of this or the we’d be still working on the project.”
Following the successful installation of the Shoalhaven River crossing, a NATA-certified pressure test was undertaken to ensure that no defects were evident in the installed pipe and that all outstanding sections of the pipeline could be tied together and readied for commissioning.
Given the very high water quality required to be delivered by the pipeline, a rigorous flushing and swabbing process was followed to ensure a clean and defect free pipeline was able to be handed over to Shoalhaven Water.
Prior to handover a further pressure test was undertaken of the entire pipeline to test all sections for conformance and ensure that it was compliant to the specifications.
Mr Horner said UEA’s work throughout the project had been to the highest standard.
“They were fantastic,” he said.
“They led us through the design process. We [Shoalhaven Water] are not experts on drilling, but they certainly indicated to us that they are.
“We’ve used them before on previous projects, so we had some knowledge of them, but certainly they demonstrated their expertise in the drilling area, without a doubt, on a very, very complex project. We would definitely work with them again.”
For more information visit the UEA website.
This article was featured in the July 2021 edition of The Australian Pipeliner. To view the magazine on your PC, Mac, tablet or mobile device, click here.
