recently, Lyttelton Road tunnel, which runs beneath the Port Hills to the south of the New Zealand city of Christchurch, was in the news marking its 50th birthday as the country’s longest road tunnel at 1,994m. Just as Lyttelton marked the anniversary, the Waterview Connection tunnels inched passed it in length, reaching 2km and taking the title for itself.
It is not surprising that Auckland is now home to New Zealand’s longest road tunnel – and the most expensive tunnel project in the country, costing NZD 1.4bn (USD 1bn). Auckland is the largest Polynesian city and has a population that is expected to continue to grow faster than the national average.
In 2002 the New Zealand government began an investment programme for Auckland’s transport infrastructure. The country’s biggest and most complex roading project – the Waterview
Connection – is due to be completed by 2017, which includes one of the country’s most challenging tunnels to-date, 2.4km of 14.1m diameter twin bores. The project is expected to reduce congestion by some 14 per cent by 2021.
The Waterview Connection will provide the final link in Auckland’s Western Ring Route (WRR). It will connect the Southwestern Motorway (SH20) at Mt Roskill to the Northwestern Motorway (SH16), providing a 48km motorway. Five years ago, the government announced it as one of the seven ‘Roads of National Significance’, because it will improve transport links and contribute to the country’s economic wellbeing.
NZ Transport Agency’s (NZTA) announced that it had chosen its preferred tenderer for the project construction in August 2011. The project attracted a high level of interest both nationally and internationally and was awarded to a specialist team, known as the Well-Connected Alliance, to manage the design, construction and operation. The consortium includes Fletcher Construction, McConnell Dowell Constructors, Obayashi Corporation,
PB New Zealand, Beca Infrastructure and Tonkin & Taylor. The consortium includes five sub-alliance partners and contractors: SICE, Wilson Tunnelling, Downer EDI Works, Boffa Miskell and Warren and Mahoney.
Most recently, the Waterview Connection project reached its halfway point. The first of the twin road tunnels on the NZTA Waterview Connection project has been completed.
Beginning the drive
Brett Gliddon, highways manager for Auckland and Northland, NZTA, explains that the launch of Alice was "extraordinary" given the complexity of the project. "Each task – which are major projects in themselves – were delivered on or within days of the exact dates they were required. They included the completion of the southern approach trench; design, fabrication, factory testing and delivery of the TBM; assembly and commissioning of the TBM on site, design, construction and commissioning of a pre-cast yard for the manufacture of tunnel lining and inverted culvert segments; and preparation of a 27ha. cleanfill site for disposal of 800,000cu.m of spoil being excavated from the tunnels." The TBM berthed at the Ports of Auckland’s Waitemata terminal in July 2013. The machine arrived in 100 separate ‘bits’ including 20 containers of small parts, where it took some 10 days to transport the TBM to the project’s southern portal at Owairaka where it was reassembled.
At 18 months into into its five-year construction programme, the Waterview Connection project was ready to start tunnelling. Alice started boring on the 31 October 2013 as planned.
"The programming and sequencing of work on this project is an enormous task. The project comprises projects within projects, all of which need to be co-ordinated and resourced," says Gliddon. "An extraordinary success was being ready to bore on the very day that had been planned more than two years earlier. Hitting the target required the completion of major tasks on the critical path, each with significant risks associated with it."
The TBM’s drive towards the northern portal began one week later. "Initial tunnelling was slower than expected but picked up substantially in 2014 with between 20 and 30m achieved most days there haven’t been stops for service extensions or cutterhead maintenance," says Gliddon.
The tunnel was a long way underground – reaching a depth a depth of 45m – to avoid the remaining volcanic rock layer. Gliddon notes: "For the most part the tunnel route passes through sandstone and siltstone that varies in strength from 1MPa to 5MPa. The machine was selected because it provided the best capability to handle the varying soil and rock conditions that would be encountered and this has been borne out by experience during the first tunnel drive."
Gliddon adds that the geology was as anticipated, with no surprises encountered. "The geology and groundwater conditions have been as expected. There was a small risk that the tunnel route would intersect layers of cemented sandstone of up to 120MPa. However, this has not eventuated."
Alice and the gantries
Tunnelling was completed with a earth pressure balance (EPB) machine from Herrenknecht. With a cutting diameter of 14.46m, Alice is the 10th largest diameter TBM in the world. The TBM alone weighs 2,400t and weighs 3,100t including the three backup gantries. The length of the TBM is 12.4m while the overall length including backup gantries is 87m. The gantries house all the equipment needed to run it, place the precast concrete rings that line the tunnels and to remove the material extracted.
The Waterview Connection project is the first time in TBM history that the installation of the services culvert and the actual tunnelling have been separated. After beginning work 500m behind the machine, the culvert gantry caught up with the TBM. Catching up with the TBM was a priority so that the culverts could provide a secondary emergency escape route as close to Alice as possible, which improves safety in the tunnel.
"A purpose-built culvert gantry is installing the culvert units for the invert culvert that will run under the motorway through the tunnels and carry the services required to operate the tunnel," says Gliddon. "This significant piece of machinery was also designed and supplied by Herrenkencht. It is 95m long and weighs 400t. The objective is to allow the TBM to run at maximum production, unhindered."
Indeed, NZTA stated that on most tunnelling projects the culvert gantry forms part of the TBM itself and the culverts are placed as the machine moves forward. The problem with this is that progress of each activity is affected by the other, which means delays with culvert placement can potentially slow down the tunnelling operation and vice versa.
Gliddon adds: "The gantry was installed in the tunnel in March 2014, with the tunnelling operation stopped. The operation of the culvert gantry has been an outstanding success. By August this year it had come as close as it can that seal the machine’s tailskin. The latter stops had been anticipated and planned for."
The TBM will now be turned around to bore the northbound tunnel. Gliddon states that the size of the machine and the limited space in which Alice has to manoever makes the turn unusual.
"The turnaround will be undertaken inside the northern approach tunnel, in an area constricted by the permanent trench structure. In fact the area for turning is just 25m by 39m.
"The TBM and backup were optimised for easier turnaround within the northern portal trench," says Gliddon. "For this reason the number of gantries is limited to just three, with the first gantry behind the TBM carrying most of the vital TBM installations."
The cutting head and its three trailing gantries will now be disconnected and each piece taken one at a time from the completed tunnel and turned. Gliddon adds: "The TBM shield and gantries will be retrieved one at a time from the completed tunnel, pushed sideways on a steel cradle, turned 180 degree and then pushed up against the entry portal of the northbound tunnel."
There is not enough space in the tunnel for all three gantries to be positioned behind the TBM shield for the relaunch. Therefore the shield, Gantry 1 and a temporary second gantry, named Gantry 2.1, will be introduced while Alice is relaunched and bores the first 300m of the second tunnel. "Gantry 2.1 will then be removed from the tunnel and Gantry 2 and 3 will be brought out of the completed tunnel, turned and positioned behind the TBM.
"Only with all three gantries in position will the main drive south resume," says Gliddon. Following this, the culvert gantry is then turned to begin installing the services culvert in the second tunnel.
Tunnelling works to construct the northbound tunnel is expected to recommence in early 2015, and preparations are currently underway to start boring the second of the twin road tunnels
