From the magazine

Least risk, most reward

Edge Underground was recently appointed to carry out a 130 m gravity sewer crossing as part of the Wedgewood Drive Relief Sewer, which involves the construction of a 1.4 km sewer running along the South Gippsland Freeway in Hallam, Victoria.

This new sewer will service future growth in the sub catchments of the abutting properties by connecting the gravity diversion sewer to the Hallam Valley Main Sewer (HVMS).

Project owner South East Water awarded the contract for the sewer transfer main installation to the Fulton Hogan Delplant Beca joint venture (FHDB), who in turn enlisted the services of Edge Underground for a particularly challenging crossing required as part of the installation.

Prevailing conditions

The crossing took place across the suburbs of Hallam and Dandenong South, known for a range of ground conditions including clay, silt, sand and a high water table.

All of these were present in the route for the crossing.

The geotechnical survey was completed towards the end of Melbourne’s recent drought, hence there were concerns about the amount of ground water and the potential for flowing ground condition.

This created an elevated risk profile for the job.

The prevailing ground conditions, combined with the fact that the bore involved 501OD HOBAS pipe under the M1, one of Melbourne’s busiest freeways, meant the job became a high risk proposition.

Axis is the answer

Vacuum microtunnelling systems are well known for their capabilities in consolidated ground clays through rock, however what is of particular interest to specialists worldwide is the ability of the Vermeer Axis guided boring system in wet flowing ground conditions.

The nature of the ground conditions in Hallam meant that a conventional vacuum microtunnelling method was considered too high risk.

However the Vermeer Axis guided boring system, whilst utilising a vacuum for waste removal, operates with a number of significant differences.

Firstly the system runs a 345 mm pilot shot which in effect provides an almost perfect geotechnical sample.

The pilot line can also utilise a range of cutting faces, which can be changed throughout the pilot shot with minimal effort.

On this particular project the concern over ground flows and the desire to create an Earth Pressure Balance (EPB) was paramount.

For these reasons Edge selected the closed face cutter, which has the ability to open or close in order to maintain face pressure.

This combined with the always cased rods allows the system to support the ground in collapsing and flowing condition.

The Axis system has been used by Edge Underground Managing Director Stuart Harrison across the globe, in Canada, the US and Europe.

The Axis system is now also being utilised in South America and is about to undertake its first project in South Africa.

Within Australia, Edge Underground has completed many projects in a wide range of ground conditions.

In particular, projects where the Axis system had a proven track record in flowing, collapsing, soft, wet ground highlighted the suitability of the system for the Hallam-Dandenong South crossing.

Mr Harrison and Edge Underground have completed projects with the Axis system, in sand and silt both wet and dry, in Bentleigh, Carrum, Morwell, Werribee, Frankston and Traralgon in Victoria.

The team has also travelled interstate with the technology, completing jobs in Townsville, Queensland; Newcastle, Gerringong and Shoalhaven Heads in New South Wales; and Mawson Lakes in South Australia to name a few.

Edge Underground has a unique understanding of the Vermeer Axis guided boring system as Mr Harrison, is the inventor of the system.

“It is not just our direct experience with Axis in Australia, it’s also about knowing what not to do with the system,” said Mr Harrison.

“The years of research and development that led to the launch of Axis, the product support we provide for Axis and our ongoing development of the system gives us unmatched capabilities with this system.

“On any job I can contact any number of manufacturers and contractors worldwide to come up with a least risk proposal in microtunnelling.”

Least risk

Least risk is a particular focus for the FHDB joint venture.

The Peninsula ECO Transfer Main Project was the first project to be completed under the newly established South East Water Alliance.

Being a gravity sewer main in bad ground and under Melbourne’s biggest freeway, it was important for FHDB that all potential risk factors on
the project were minimised.

For the crossing it was established that the least risk contractor was Edge Underground; the least risk method was the Axis guided boring system; the least risk timing was to complete the project in dry weather and timed to allow continuous operation on the pipe installation; and the least risk pipe to use was HOBAS jacking pipe.

As a result, and thanks to the depth of experience on site, the crossing operation went like clockwork. Every aspect of the bore was pre-planned and allowed for in advance.

Ongoing works with Edge Underground and the FHDB joint venture, as well as the individual companies comprising the alliance, are testament to the overwhelming success of the project.

As experts in the installation of precision trenchless pipelines, Edge Underground see that it is their responsibility to create trenchless solutions to reduce risk and provide successful outcomes to all vested parties.

Contingency planning, risk management, contractor and equipment selection are all key ingredients in the Edge Underground contracting service

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