Rapid excavation breaks through in Brisbane

First breakthrough is achieved on the 4.6km Legacy Way traffic tunnel in Brisbane, Australia. TBM Joyce, the first of two refurbished 12.4m diameter Herrenknecht Mixshields used for the project, holed through the head wall yesterday (24 April 2013).

Progress has been rapid throughout the drive, which has recorded a best daily advance of 49.7m, a best weekly advance of 248.8m, and a best 30-day progress of 858.1m.

“This is an outstanding performance and there are only a few projects worldwide that can show similar achievements using large diameter TBMs,” said Transcity Tunnel Construction Manager Matteo Ortu of Ghella.

The drive is completed in just six months, at an average rate of more than 20m/day. Transcity, a JV of Ghella (Italy), BMD Constructions (Australia) and Acciona (Spain), will now dismantle the machine ahead of sale back to its original manufacturer Herrenknecht.

TBM Annabell, which launched from Toowong site on the parallel tube in November 2012, is expected to achieve breakthrough at the Kelvin Grove end in June 2013. Both machines were rebuilt and modified for Legacy way (previously known as the Northen Link) after having completed the 6.8km CLEM7 traffic tunnels under the Brisbane River three years ago.

A spokesman for project owner Brisbane City Council, said: “ Joyce has completed a record-breaking journey that has seen her travel the 4.6km in just six months. She has excavated an average of 150m/week, which is an outstanding feat for any tunneling project using machines the size and scale of those used on Legacy Way”.

Work continues on construction of the 36 cross passages that link the parallel tunnels. Matteo Ortu said two specialised remote control rock hammers, a Brokk 400 and a Brokk 800, have benn specially procured to excavate them.

“The advantage of using Brokks is their capacity to operate in confined spaces, while still achieving the same performance as larger excavators, and their remote control safety features”, said Ortu. A half tonne or 1.2 tonne variable frequency hydraulic rock breaker is fitted to the retractable arm of the Brokk and allows the team to safety axcavate each passage”.

Once the Brokk has completed excavation, rock bolts are inserted into the cross passage walls and shotcrete is applied to the inside to provide added support prior to waterproofing and fit out.

Currently four cross passages are excavated and are now undergoing reinforcement and waterproofing, with completion of the remaining 32 scheduled for early 2014.

Spoil conveyor tunnel

Once of the more unique features of the Legacy Way project has been the use of a specially excavated 530m tunnel, constructed in advance of TBM launch, into which an 830m – long spoil conveyor is installed to transport the estimated 1 million m3 of muck generated from excavation of the main TBM – driven tunnels directly to a nearby quarry site. The spoil conveyor tunnel took four months to construct using conventional drill+blast, and runs from the western worksite at Toowong directly to the Mount Coot – tha Quarry.

The environmental benefits have been enormous, with an estimated 96,000 truck loads saved. Constructing an over land conveyor as was originally planned would have meant having to destroy a hectare of vegetation.

Transcity Project Director Fernando Fajardo said construction of the spoil conveyor tunnel (completed in March 2012) had also provied a unique opportunity to test various methodologies for construction Legacy Way’s key tunnel infrastructure, including the cross passages”.

Transcity was fortunate enouth to test rock hammering and controlled blast methodologies before work started on the Legacy Way tunnels, enabling the team to better understand ground conditions and the machinery required to construct features like cross passages”, said Fajardo.

Legacy Way is Brisbane’s third major road tunnel project, following the 6.8km Clem Jones (CLEM7) Tunnel and the recently – opened Airport Link. It forms the fourth part of an overall trasport plan known as the TransApex ring road program.

Peter Kenyon

Brisbane advanced vital traffic link – TunnelTalk, November 2012
Rebuilt TBMs launch on Brisbane traffic tunnel – TunnelTalk, August 2012
Brisbane awards Northern Link highway – TunnelTalk, September 2010
Northern Link plan of attack – TunnelTalk, September 2010