The Connectus JV is constructing a bridge to maintain traffic and people flows while protecting Auckland’s utility services.
Auckland’s City Rail Link (CRL) is the biggest infrastructure project in New Zealand and is taking place in a busy inner city environment full of traffic and people. It’s essential to keep the city moving throughout the construction works.
High volumes of pedestrians and traffic use the Customs-Albert intersection, under which the CRL’s twin tunnels will run.
Also under this intersection are high volume eftpos and internet cables, electricity cables, stormwater, water and sewerage systems, servicing the high-end retail, hotel, businesses and apartments of a modern global city. Like the road and pedestrian traffic, they must continue to operate seamlessly.
So how can this be achieved when a 14-metre-deep trench needs to cut through a location used by a quarter of central Auckland’s public transport passengers and thousands of workers, residents, tourists and shoppers every day? The answer is: carefully constructing a bridge in stages.
The challenges faced are not small, as Lance Vazey, bridge deck project engineer, says.
“This job needs extra attention as the utility services are live. A moment’s inattention and we can shut down the water, gas, internet or the electricity to Auckland’s CBD or even worse, hurt someone. So we get it right, safely.”
The task for Connectus (the McConnell Dowell and Downer joint venture) is to prepare for the excavation of the twin tunnels along Albert Street from Customs Street to Wyndham Street, which will start at the beginning of next month (July).
The Customs Street junction deck sections make it look like the Connectus JV is rebuilding the road in pieces. But within two months these pieces will become an underground bridge to protect Auckland’s utility networks and keep traffic flowing. The team will excavate 14 metres under the bridge and the tunnel boxes will then be built at this depth.
The bridge is constructed in four sections, each taking up to three months to complete. Two sections have already been completed. The third section will be completed in July and the fourth section will be constructed from July to September 2017.
The first stage of the construction bridge is to excavate each section. A temporary timber retaining wall is built around the section to support and secure the wall against the road. The utility services are then supported and protected to ensure there is no disruption to local residents and businesses.
Once this is completed, the construction of the deck section can start. Underneath the utility services, the ground is poured with site concrete before installing the steel structure and backfill with structural concrete. This reinforces the base of the deck section for traffic and will protect the utility services from the excavation of the tunnels.
A timber framework is them formed to backfill the deck section up to the road, which is then filled with flowable fill, a low-density concrete.
Final steps are to backfill the deck section with aggregate and several layers of asphalt before being marked up and reinstated, ready for use by the public.
“This intersection is one of the busiest in New Zealand in terms of pedestrians and cars,” says Lance.
“Each deck section requires a new traffic management layout, with barriers shifted, line marking, lights and traffic controllers to assist pedestrians. The space is very tight between the work area and the public so we need to be very careful.
“The noise is also a big challenge, as this area is surrounded by residents and shops. They are also our priority and we try our best to limit the noise so they are not too impacted by the work.”
The result is Auckland keeps moving while the Connectus JV excavates the CRL 14 metres beneath them.