Victoria Park Tunnel is a 450-metre ‘cut and cover’ tunnel next to the Victoria Park Viaduct, to take three lanes of northbound traffic. Through St Marys Bay the motorway is being widened by one lane in each direction, to give 10 lanes in total. A bus shoulder lane will be re-established in the citybound direction.
At the end of the project the existing Victoria Park Viaduct will be reconfigured to take four lanes of southbound traffic.
Tunnel construction
The cut and cover tunnel is, in effect, a very large trench with a roof over the top.
Once the roof is on, normal activities are put back on top. In the case of the Victoria Park Tunnel, this will include reinstating grass and trees on top of the section of tunnel through the park, putting traffic over the top of the tunnel where it runs under local streets and moving the Rob Roy Hotel back to its original site, which will then be on the roof of the tunnel’s southern portal.
We are therefore increasing the capacity of the motorway without taking away precious green space in central Auckland or the landmark Rob Roy Hotel.
Construction challenges
The cut and cover construction method is the only practical solution because of the relatively shallow tunnel route. It also allows construction in many places simultaneously, saving cost and time.
The tunnel route starts near Franklin Road, behind the site occupied by the Rob Roy Hotel. From there it crosses Victoria Street and goes through Victoria Park, next to the Victoria Park Viaduct. At the northern end of the park it passes under Beaumont Street before exiting as part of the Fanshawe Street motorway on ramp.
Much of the route is through land reclaimed in the early 1900s from the original Freemans Bay and the St Marys Bay foreshore. The ground conditions encountered as construction progresses through this reclaimed land will be particularly challenging. In particular, the high water table means any structure in the ground runs the risk of rising up or ‘floating’ due to the water pressure.
The base of the tunnel is up to 12 metres below the existing ground level. Deep piles will extend a further 10 metres into the bedrock to prevent the floating.
The tunnel width ranges between 16 and 18 metres.
Construction process
The tunnel is being built from the top down in the following stages:
Services like water pipes, electricity and communications cables are diverted away from the tunnel route. This includes moving the Rob Roy Hotel, which sits over the site of the tunnel’s southern portal.
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Services, including the old Rob Roy Hotel, had to be moved away from the tunnel route before construction began.
Guidewalls are installed on the line of the tunnel walls.
Drilling rigs, cranes and excavators arrive on site to build tunnel walls from the surface down. Two wall construction methods are being used – secant piles from the centre of Victoria Park north and diaphragm panels from the centre of the park south.
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Secant pile walls were built where it was possible to drill into underlying sandstone.
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Diaphragm panel walls have been built through soft ground, such as the reclaimed Freemans Bay that is now Victoria Park.
Roof beams are installed between the walls to hold them in place.
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Roof construction follows wall construction in the ‘cut and cover’ construction sequence.
Excavators remove dirt and rock from between the walls.
The tunnel floor is built and anchored into the bedrock below.
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The tunnel trench is dug out only after the walls and roof are in place to provide a solid framework for the tunnel.
Services such as lights, fire protection systems, emergency exits and ventilation fans are installed. The tunnel is opened to traffic.
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Pouring the floor of the tunnel closely follows tunnel excavation.
Managing Construction Effects
Construction management plans are guiding construction activities - in particular traffic, dust, noise and vibration – to minimise the adverse effects of construction in accordance with designation and consent conditions and Transport Agency guidelines.
Tree protection
Spectacular pohutukawas grow on the St Marys Bay cliffs. In the planning the motorway widening and construction methodologies, care has been taken to minimise impacts on trees. However, some trees will have to be removed and others will need to be trimmed. Those that remain will be protected and regularly monitored by a qualified arborist to assess their on-going health.
Erosion and sediment control
Works are being staged to expose only the areas required immediately for construction. Where earthworks have been completed, they are stabilised using hay mulch, roading metal, grass or landscaping to stop erosion.
Protecting the marine environment
Clean stormwater and the harbour are protected from sediment discharging from the site by using controls such as silt fences, filter socks and decanting earth bunds (as per Auckland Regional Council’s TP90 guidelines). A higher level of treatment for stormwater from the finished motorway surface will be installed as part of the project.
Experienced, trained staff
A dedicated environmental team is on site to direct workers in environmental management and to provide ongoing environmental training.
Dust
We control dust from our earthworks by reducing the area exposed to the weather at any one time and by stabilizing areas as we go. We also monitor dust generation daily and use water trucks to dampen problem areas when necessary. Roads are regularly swept to reduce surface dust.
Contaminated land & groundwater management
Past activities – including gas production - and uncontrolled reclamation in the Victoria Park area have left some residual contamination which is carefully managed during construction.
Contamination outside of the Victoria Park area - along St Marys Bay for example - is not expected to be as significant and is fairly typical of motorway swales and shoulders. However excavations through some areas of the site may still encounter contaminated material and groundwater. The team does regular soil and groundwater monitoring to detect this. Contaminated water on site is captured, treated and discharged to trade waste. Contaminated solid material is separated out and taken to a disposal site licensed for that waste.
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A photograph from the early 1900s shows the historic gas storage tanks formerly located on the corner of Franklin Road and Victoria Street.
Noise
The Victoria Park Tunnel project has a management plan that addresses all aspects of construction noise and vibration.
The project involves targeted consultation and communication with those potentially affected. Noise management measures can include temporary noise barriers, using alternative equipment if possible and, where possible, scheduling construction for certain times or days.
Night time work is required from time to time, usually to complete work that cannot be done while the motorway is open. We plan in advance to minimise these night works as much as possible and advise residents accordingly.
Air quality
The completed project will help alleviate traffic congestion. It therefore will reduce air emissions by reducing the 'stop-start' traffic flows that contribute to increases in vehicle emissions. The tunnel will be ventilated to manage build up of emissions.
Traffic management
We are required to maintain traffic flows on the local roads and motorways during the project. And although we know it is challenging, we are committed to causing minimal fuss and disruption.
We do this by staggering construction and only reducing motorway capacity where necessary during lower traffic times, such as at night and during the weekends.
We constantly monitor travel times throughout the project and buses continue to run according to schedule.
Although there will be occasional diversions at the Victoria Park area there will be minimal impact on the traffic.
We will be issuing on-going updates through our website, the media and our newsletters to make sure local businesses and residents are constantly kept informed of any changes on motorway and local roads.
