The Northern Sewerage Project (NSP) is an $A650 million essential infrastructure project. It involves the construction of 12.5 kilometres of new sewer from Reservoir to Pascoe Vale, and is an investment in Melbourne’s future. John Holland is responsible for constructing both stages of the NSP on behalf of the project’s clients Melbourne Water (Stage One) and Yarra Valley Water (Stage Two).

Since construction works commenced on the NSP in August 2007, the project has achieved a number of significant milestones. Site establishment and shaft excavation works have been completed across all eight major project sites, including the five day time and three 24 hour shafts. Large acoustic enclosures have been erected at each of the 24 hour sites to allow for 24 hour tunnelling operations in densely populated urban environments.

Why the TBMs were selected

Considerable geotechechnical investigation undertaken prior to construction formed the basis for tunnelling and shaft sinking methodology, and machinery selection. The mixed face Earth Pressure Balance (EPB) tunnel boring machines (TBM) were selected to allow for operation in both pressurised and non-pressurised modes to cope with varying ground conditions whilst the hard rock TBM was the most suitable for the conditions encountered on Stage Two.

The project so far

Mr Muley says that one of the major challenges facing the project overall was the simultaneous launch and concurrent operation of two TBMs out of the 65 metre shaft at Brearley Reserve. Gemma, a four metre diameter Herrenknecht EPB TBM, commenced tunnelling south to Vanberg Road in May 2008, at the same time as Victoria, a three metre diameter Herrenknecht EPB TBM, which began tunnelling northwest to Bass Street.

Additionally, Gemma was required to excavate through interface zones ofrock, sands and clays under high risk areas, including CityLink, one of Melbourne’s major freeways and a vital link in the city’s transport infrastructure.

These challenges were overcome through a combination of detailed/staged launching methods and the pre-excavation of 80 metre launch chambers. A vertical conveyor is used to transport spoil to the surface to ensure efficient production. The project undertook real-time monitoring of CityLink and immediate transfer of information during the freeway crossing, during which no settlement was recorded.

Completing the NSP

The project has now completed five of the seven required tunnel drives, with the last three of these recent tunnel breakthroughs occurring within a busy three to four week period, from September to October.

The two tunnel drives still to be completed include Gemma excavating the project’s longest tunnel drive, the 2.9 kilometre long tunnel running from Brearley Reserve to Carr Street; and, Victoria excavating the final 715 metres of the 1.3 kilometres Newlands Road to Carr Street tunnel. The first 600 metres of this tunnel was excavated using controlled drill and blast methods.

Both these tunnel drives are scheduled to commence late 2009 and are due for completion in 2010.

Once the tunnel drives are excavated the next phase of construction involves pipe lining installation, which consists of GRP pipes being set to their final position in the tunnels, using grout to fill the remaining space between the pipe and the excavated tunnel.

Pipe lining installation is required along the entire tunnel alignment, with works having already commenced at different stages across the project; including the De Chene Reserve to Carr Street tunnel drive, and the Newlands Road to Jukes Road drive.

The project is timed for completion in mid-2012.

JULIA'S MEASUREMENTS

Weight: 228 tonnes

Length: 93 metres

Diameter: 3 metres

Julia is a Robbins Rock Double Shield TBM. Trenchless Australasia spoke with Julia about her journey under the northern suburbs of Melbourne building the NSP.

What is the length of the drives completed so far?

I have completed two tunnels on the NSP; a 2.1 kilometre tunnel followed shortly after by a 1.1 kilometre tunnel.

Tell us about the journey

I commenced tunnelling the 2.1 kilometre drive from Newlands Road, Coburg North, in January 2009, achieving breakthrough at Jukes Road, Fawkner, on 2 July 2009.

Following a short maintenance break, I recommenced tunnelling, heading further northward on the 1.1 kilometre tunnel from Jukes Road to L.E. Cotchin Reserve, Reservoir. I reached the 39 metre vertical access shaft at L.E. Cotchin Reserve on 3 October 2009.

The depth below surface of these tunnels ranges from 30–40 metres.

What are the ground conditions on Stage 2 of the project?

Ground conditions along Stage 2 of the project differ considerably from those on Stage 1, with the geology varying from massive columnar basalt to a mixed face of weathered basalt with infilled clay seams. I am an American-made Robbins Hard Rock TBM employed to cope with these specific conditions.

VICTORIA'S MEASUREMENTS

Weight: 250 tonnes

Length: 92.5 metres

Diameter: 3 metres

Victoria, is a Herrenknecht TBM, she enjoys working in varied ground conditions under the suburb of Coburg.

What is the length of the drives so far?

I have completed two tunnels on the NSP, each are 1.6 kilometres in length.

Tell us about your travels.

I started tunnelling the 1.6 kilometre drive from De Chene Reserve, Coburg, in May 2008, achieving breakthrough at Carr Street, Coburg North on 2 December 2008.

I was then transported to Brearley Reserve, Pascoe Vale South, where I began tunnelling the 1.6 kilometre drive to Bass Street, Pascoe Vale, in May 2009. I reached the 30 metre vertical access shaft at Bass Street on 9 September 2009.

The De Chene Reserve to Carr Street tunnel ranges from 18–37 metres in depth, while the Brearley Reserve-Bass Street tunnel reached greater depths of between 30–64 metres. The Newlands Road-Carr Street tunnel will be excavated at depths of between 31–37 metres.

I am due to commence my third drive in late 2009, excavating the final 715 metres of the 1.3 kilometre Newlands Road to Carr Street tunnel. The first 600 metres of this tunnel was excavated using controlled drill and blast methods.

What are the ground conditions?

The ground conditions varied from 200 MPa basalt, to siltstone, sands, clays and soils. John Holland Group managed these ground conditions using me, a mixed face EPB TBM, as I am designed for optimum operation in both hard rock and soft ground conditions.

GEMMA'S MEASUREMENTS

Weight: 300 tonnes

Length: 99 metres

Diameter: 4 metres

Gemma is a Herrenknecht EPB TBM, she enjoys the challenges of the project such as tunnelling under the freeway, CityLink.

How far have you tunnelled for the project?

I have, thus far completed a 1.8 kilometres tunnel on the NSP.

In late 2009 I will commence my next tunnelling challenge, excavation of the projects longest tunnel drive, the 2.9 kilometre tunnel drive from Brearley Reserve Pascoe Vale South, to Carr Street in Coburg North.

Where are you launched from?

I commenced tunnelling the 1.8 kilometre drive from Brearley Reserve, Pascoe Vale South, in May 2008, reaching the 18 metre vertical access shaft at Vanberg Road, Essendon, on 7 September 2009.

The depth of the Brearley Reserve to Vanberg Road tunnel ranged from 18-64 metres.

What are the ground conditions?

The ground conditions vary from 200 MPa basalt, to siltstone, sands and clays. A mixed face EPB TBM, such as myself, is designed for optimum operation in both hard rock and soft ground conditions.