Page 8 - TunnelTalk Annual Review 2014

Gas detection protection
ATrolex gas detection system on the project’s TBM monitors oxygen, CO2, CO, NO2, nitric oxide and hydrogen sulphide levels. In addition the system monitors for potentially explosive methane at four locations around the TBM. Information from all detection systems is routed to the machine’s main control panel and is powered by a Trolex power supply complete with battery back-up to enable it to continue operating in the event of a power shutdown on the TBM.
The Trolex system provides continuous real time gas readings with pre-programmed limits that automatically set off alarms in the control cabin if any are exceeded.
In addition to protecting the Herrenknecht TBM, Trolex has supplied the Well Connected Alliance with a separate fixed gas detection system for the tunnels using 12 Trolex Sentro 8 units with battery back-up and ethernet connectivity. These monitor for NO2, oxygen and CO.
Phil Elliott, CEO of New Zealand Trolex distributor Cuthbert Stewart Ltd (CSL) said, “We have provided a
TBM mounted gas monitors
complete end-to-end solution including commissioning and calibration through the full project period. Technicians visited the project to commission and calibrate bothsystemsandalsoprovidedtraining for the installation.”
In 2014 Trolex protective systems were deployed on more than 50 TBMs around the world. n
Waterview connection will complete a vital western bypass of Auckland city centre
Precast segment manufacture
steel plates, welded together to ensure a smooth, airtight surface.
Appropriately enough a grease compound to ensure minimal friction between the cradle and the steel plated floor contains lanolin extracted from the wool of some of the country’s 80 million sheep. “The back-up gantries will be turned in the same manner and we expect to complete the process within three months,” said Hanke.
Precast steel fibre reinforced concrete segments measuring 2m x 450mm thick are supplied to the project by a sub-Alliance contract with Wilson Tunnelling from a fabrication plant in Auckland. Each ring comprises nine segments and a key, for a total of more than 24,000 segments for both tunnels. Additionally 2,400 inverted U-shaped precast concrete culverts measuring 2m long x 3.7m wide x 2.22m high will be manufactured at the same casting yard to run under the road deck.
In addition to supplying the TBM, Herrenknecht also supplied a continuous conveyor mucking system. With each metre of advance producing 164m3 of muck, a loco and skip mucking system would have been inadequate. Muck disposal is via truck from a fully enclosed on-site spoil building to a disused quarry some 18km to the south.
As the turnaround procedure progresses, second-stage backfilling to road level will be carried out in the completed tunnel. A first stage backfill, to the upper level of the U-shaped culvert segments installed in the invert behind the TBM, was completed by a standalone back-up gantry that followed the advancing TBM. Secondary backfill will be to a depth of 1.2m above the top deck level of the culvert.
Excavation of the 16 cross passages at 150m intervals along the 2.4km underground alignment will take place as the TBM advances along its return drive. Pipe arch presupport will support excavation of the cross passages. n
References
• New Zealand awards mega-TBM undertaking - TunnelTalk, August 2011
that the tunnel passes with 7m of cover under a major six-lane highway.
“We could have advanced faster but we deliberately slowed the TBM to about five rings/day for the last 200m through the area of lower cover. During this time we held daily briefings with our design and geotechnical teams to agree our drive parameters for the day. We reduced the face pressure to about 0.8 bar to ensure that we avoided any blowouts to the surface, and had to ensure at all times that we had the balance between face pressure and settlement right.”
At times settlement under the reduced
cover was recorded at 25mm, “not too bad,” according to Hanke, for under the Great North Road that is one of the busiest in Auckland. In fact, a special chicane was constructed to divert the path of the highway to ensure it was never directly above the tunnel face.
The next challenge for the team was managing the turnaround of the 87m long TBM shield and its three back-up gantries in the narrow 39m x 25m northern approach trench.
The 12.4m long TBM shield will be turned on a steel cradle using hydraulic jacks and across a covering of heavy
From left: Mega-dimensions of Waterview highway tunnel; Invert roadway gantry; View into the heading from the southern portal
8
TunnelTalk AnnuAl Review 2014 www.TunnelTalk.com
MEGA PROJECTS
PREVIEW