The Manawatu Gorge section of State Highway 3 is one of the most difficult roads in New Zealand to work on
This narrow road is carved into the side of the Manawatu Gorge 20 metres above a river. The road is a vital transport link for communities on the east and west of the central North Island. In October 2011, a destructive landslide struck. Measuring 140 metres wide and with a crest 130 metres above the road, this is the largest road landslide in New Zealand’s history. Stantec was the New Zealand Transport Agency’s (NZTA) network consultant and geotechnical engineer for the project. Together with a team of specialist geologists, geotechnical engineers, the client manager and contractor, we worked collaboratively, and with urgency, to reopen the highway.
Stantec was responsible for management of the project to reinstate the highway and make the route safe and to conduct a geotechnical analysis to identify the safest option for remediation of the landslide scar. For there, our team also created the geological and excavation models to define a safe slope profile and monitor the clearance work as it was undertaken, created modelling and risk analysis, designed the mesh drape and development of the rock fall attenuator fence, and created a road alignment design.
The work carried out to stabilise and remediate the Manawatu Gorge slip has been a huge undertaking by all parties involved. While the initial slip was considered large, the on-going regression and final remedial design was far bigger than anyone initially anticipated. A collaborative team approach resulted in an expedient response and the safe removal of the slip material from the site.
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