Coogee to Alexandria Land Based



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Project Overview

A 14,000 kilometre continuous new telecommunications fibre optic cable has been installed spanning across the Pacific Ocean directly connecting the USA and Australia with landings in Portland, the United States, New Zealand, American Samoa and Sydney. With the landing on the south side of Coogee Beach, a conduit was required from the ocean outfall to a recently built data centre in Alexandria.

Scope of Works

UEA installed 8,620 metres of single 125mm HDPE using HDD methods. Once the conduit was laid, 57 haul pits and five splice pits – including earthing – were installed. Ground conditions varied between Sydney sandstone and water charged sand along the entire route.

Construction

As the bore lengths ranged from 50 metres to 245 metres, UEA operated up to three HDD rigs at once: Vermeer D60x90, Ditchwitch AT4020 and a AT3020. A civil crew then worked full time to link up bores, install pits and restore all sites.

Challenges

The new conduit route required crossing major Sydney roads including Anzac Parade, Southern Cross Drive, Gardeners Road, O’Riordan Street and along Bourke Road. These roads are major arterial routes – not only for transport, but also for other utilities including high voltage electricity, high pressure gas and major fibre optic networks. Because of this, the planning of alignment and depths required significant upfront investigation and consultation with existing utility providers. Every service was traced, rodded and potholed along the entire route to ensure an alignment was achievable. UEA’s team started this investigation a month before drilling commenced using a vacuum excavation, and monitored the situation throughout the duration of the project.

Ground conditions varied from sandstone in Randwick to sand in the Coogee and Alexandria areas. These changing ground conditions required different drilling techniques, utilising inner rod rock drilling with sandstone and specialist drilling products for drilling in water charged sand to maintain the hole integrity.

UEA encountered contaminated material on multiple sites throughout the project, and the team routinely conducted extensive testing to ensure correct tracking and disposal of this contamination. Drilling waste was stored securely at UEA’s onsite facility during testing, and if the material was deemed as contaminated, a specialist transport company was engaged to dispose of material as per EPA requirements. The contaminated material also affected the impact of the drilling products. Additional specialist products were utilised to ensure the bores could be completed.

One significant bore was located under the Australian Golf Course and Southern Cross Drive crossing, totalling 220 metres through water charged sand. The client imposed restrictions in relation to the proximity to an existing high voltage electrical cable, and in addition the golf course did not want the new cable under the golf green. After an open dialogue with the golf course, UEA was able to design the bore path and access the course while tracking the bore, and ensured that the hole held up and avoided frac out on the property – all parties were satisfied with the end result.

The majority of this project was undertaken within residential streets, requiring a close working environment with residents and high foot traffic. Full time traffic control ensured the safety of both pedestrians and workers throughout the job. Affected residents were notified with a letter drop before crews started on site, which detailed of the scope of work and how the project would be conducted.

The airport link train line runs directly under Bourke Road, which has a clearance that limits the depth of drilling to a maximum of five metres. As such it was required that work under the canal be minimal, and this caused risk of frac out. To combat this risk, the bore was reduced to the minimum distance to alleviate in-hole pressure. Every time the train passed, the ground also vibrated, causing the sand hole to collapse and grip the rods. Bores were shortened to reduce the time the rods were underground, and a new mud mix was created in order to complete all bores along Bourke Road.

Completion

All pipework work was proven with a mandrel and roped. UEA located all pipework and pits with GPS using internal resources, and then a work-as-executed plan was drawn up on CAD to present to the client. With co-ordinates and levels provided as part of the work-as-executed plan, it will be easier to locate the conduit with a high degree of accuracy for any future work required.