Project Overview
- Excavation contractor: Jayelle Pipelines
- Microtunnelling contractor: Edge Underground
- Pipe supplier: HOBAS, OD427 mm pipe
Melbourne’s Victoria Harbour is receiving a new, integrated precinct that includes housing and commercial buildings. The partnership owners of the project will be delivering “÷Dock Square’ – a new civic hub and community centre.
With the development of new high-rise buildings and apartments comes the need for new associated water and wastewater infrastructure to provide them with service. As part of these works, a new gravity sewer was installed that runs from the new wharf’s edge to the Collins Street end of Melbourne Docklands.
The Victoria Harbour Sewer Reticulation Project
The project was located in the Docklands, which construction contractors would readily recognise as being renowned for its water-saturated Coode Island silt. Additionally, the land was reclaimed in the early 1900s, and as a consequence the underground terrain contains miscellaneous debris from early establishment on the site. Any construction method chosen would have to not only keep the aboveground developments in pristine condition, but also contend with an installation 3 m below sea level through a pipe route with unknown obstacles.
Edge Underground was able to provide a solution to these difficult project constraints by the use of key-hole pipelining with microtunnelling. While an open-cut installation method would scar the terrain as adversely as open-heart surgery on a patient, key-hole pipelining could be likened to key-hole heart surgery, a safer, cleaner alternative.
Edge Underground Owner Stuart Harrison said “A trenched solution would have required constant dewatering of the trenches. Microtunnelling only required dewatering in the working shafts, generating cost-savings, and an ease of installation – not to mention serious time savings and minimal reinstatement.”
It would have posed a significant cost to treat and dispose of contaminated
soil. By using boring instead of open-cut, the project owners were given a solution that would greatly reduce the contamination in roughly the same installation time frame.
There are also a lot of services that currently run through the Docklands, so the project owner wanted to use a method that would bypass these services and could install underneath them without disrupting them or running
into them.
The right instruments
Edge Underground used the Vermeer AXIS Guided Boring system for the project. This system was the preferred option due to the complexity of installation. The gravity sewer had a small diameter of OD427 mm, collapsing below the water table marine silt.
Mr Harrison said “There was the very real potential of multiple and various obstructions requiring some unique drilling capabilities and minimal shaft sizes. We chose the AXIS package because it has a history of success in challenging ground conditions.”
All of the bores were installing HOBAS OD427 mm pipe, with the line lengths varying from 26-67 m in length.
Operating on a difficult patient
Mr Harrison said “The most challenging aspect of this project was the complexity of the ground. Very wet low-blow count marine silt combined with many obstructions, like timber pylons, concrete and brick structures, meant using some ingenuity with our equipment.
“We needed to set up for soft-wet conditions, which typically require closing the cutter-face. However, we still required serious cutting and removing capability, which requires opening the cutter-face and running aggressive cutter configurations that have serious extraction capacity. These are completely opposing configurations.
“With AXIS we have a soft ground head and a consolidated ground head, each of which can run a variety of cutter configurations. Over the first two lines we trialled two different combinations to assess the preferred method for the works. From Bore 3, the set-up remained constant.
“All bores were completed successfully; however, the last pipe of the first bore required resetting due to a loss of ground pressure. The typical accuracy was +/-10 mm,” said Mr Harrison.
In four of the six lines Edge Underground struck obstructions, with a total 15 timber pylons encountered, as well as many brick and concrete structures. All of the obstructions were drilled through without the need for any further excavation works.
Mr Harrison said “On numerous previous works in these conditions, the norm is to excavate and remove in order to complete the line. We believe the capabilities of the AXIS system to pass through obstructions are unparalleled.” Removal of obstructions via excavation has a very detrimental result on cost, timeframes and overall disruption to the project – the fact that this wasn’t required has meant great success for
the project.
Future outlook
The main line was completed by Edge, and the company are in negotiations to now complete further ancillary lines with the AXIS system. Contingency plans for the project were laid out, however, they were not required.