Manawatu Gorge Landslide Remediation

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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 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.

    Location: Manawatu, New Zealand
    Region: Asia Pacific
    Service Offering: Engineering & Design
    Market Sector: Transportation
    Status: Complete

    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.

    MWH Global 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, client manager and contractor.  MWH worked collaboratively, and with urgency, to reopen the highway.

    MWH was responsible for:

    • management of the project to reinstate the highway and make the route safe
    • geotechnical analysis to identify the safest option for remediation of the landslide scar
    • creating the geological and excavation models to define a safe slope profile and monitor the clearance work as it was undertaken
    • modelling and risk analysis
    • design of the mesh drape and development of the rock fall attenuator fence
    • 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 comprehended. A collaborative team approach resulted in an expedient response and the safe removal of the slip material from the site by the end of May 2012. The road was opened to two-way traffic on 19 September 2012.

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    “The crew have stuck at the task for a long time, and they can now reflect on a job well done. They’ve rebuilt an entirely new piece of highway in a superbly orchestrated blur of activity, and words can’t express the value of their hard work for the Manawatu region and beyond. Every cliché about true grit and Kiwi ‘number eight wire’ ingenuity comes to mind, but at the end of the day, they had a job to do – a huge job – and they did it.”

    David McGonigal, NZ Transport Agency Palmerston North State Highways Manager

    • Project management
    • Geotechnical analysis
    • Geological and excavation model development
    • Modelling and risk analysis
    • Design of rock fall mitigation measures
    • Road alignment design
    • September 2013, winners of the Medium Road Project at the Roading New Zealand Excellence Awards for the clearance and reinstatement of State Highway 3 following the October 2011 Manawatu Gorge landslide
    • 17 October 2011 – Large slip closes road around 370,000m³ of material
    • 10 November 2011 – Completed analysis and assessment of options to gain access to clear the site and analysis and modeling of safe slope line
    • 11 May 2012 – Slip material all cleared
    • 31 May 2012 – Road opened to one way traffic using temporary road
    • 22 June 2012 – Safety netting installed
    • 25 July 2012 – Bridge 8 completed
    • 29 August 2012 – Road opened to one lane traffic
    • 7 September 2012 – Retaining wall finished
    • 19 September 2012 – Road opens to two way traffic
    • 27 October 2012 – Colluvium works completed
    • 2 November 2012 – Attenuator fence completed




    Our address

    Manawatu, New Zealand
    -40.3854367, 175.71312690000002

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