24 September 2018 | Transmission Gully Project | Article
The design and construction of Transmission Gully to withstand a significant natural disaster is a key objective for the NZ Transport Agency.
NZ Transport Agency Senior Manager Project Delivery Chris Hunt says it is critical that the new motorway is resilient and can provide a lifeline route to and from Wellington in the event of a significant storm or earthquake.
“Route resilience was specified by the NZ Transport Agency as a critical component of the Transmission Gully project at the very outset. Wellington is well known as a seismically active region and as such all designs have been developed with this in mind.”
Wellington Gateway Partnership Project Manager John Humphrey adds that the design not only ensures that the road and structures can withstand multiple significant events, but also ensures that access along the route can be quickly reinstated post-event.
“The motorway has been designed in such a way that will allow access for emergency vehicles and supplies in a mere matter of hours – instead of the much longer period that it would take along the current route.”
“Bridges have been innovatively designed and will be built to move with the earth and therefore withstand a significant earthquake and earth stabilisation techniques along the route have been applied to areas of the project based on site-specific geotechnical conditions.”
Benching, rock-anchors and Shot Crete are techniques that have been used to influence how the road and surrounding environment behaves, simplifying the need to respond and repair the road.
“The four lanes along the length of the motorway mean that even significant debris falls will block only some of the lanes, not the entire route.”
New Zealand engineers are at the forefront of building for seismic resilience, applying learnings from both Christchurch and Kaikoura earthquakes to the design and build of the 27km Transmission Gully project. Seismically resilient design and building processes used throughout the project aim to ensure earthworks and structures will either withstand quakes or be easily re-instated.
For example, Cannons Creek Bridge, the project’s largest structure, is being built on large base isolators like those that can be seen at Te Papa and Wellington Hospital. These ‘giant rubber pads’ allow the structure to move with the earth, a process which has been proven to improve the ability of structures to withstand significant seismic events. It is a world leading approach to structural resilience and at Transmission Gully it involves world-leading expertise: the Cannons Creek Bridge isolators are built in Spain to exacting specifications from New Zealand and Australian engineers, they are tested in Los Angeles before being shipped to New Zealand for installation.
In a subsequent project newsletter we’ll look at how aspects of design and construction support the Transmission Gully motorway’s long-term resilience, including ease of road maintenance.