Manawatu Gorge Landslide Remediation

In October 2011, the largest landslide in New Zealand’s history, to affect a roadway, caused devastation to State Highway 3, within the Manawatu Gorge. The 370,000 cubic meter slip, closed the major transport route and damaged two existing bridge structures beyond repair. A third bridge received minor damage and was able to be successfully repaired, while highway realignment required a fourth existing structure to be widened.

The NZ Transport Agency engaged BBO, through our existing Bridge Management Contract, to complete conceptual design, gain client acceptance, arrange and oversee geotechnical investigation, and the detailed structural design and specification for a new 51m long bridge and 82m long tied back retaining wall. This also included repair to an adjacent bridge damaged by the slip and widening of an original 1926 half bridge, to improve the carriageway width and straighten the road alignment; thus improving the driving experience through this rebuilt section of the gorge.  BBO worked collaboratively with an equally determined team from MWH and Higgins to reinstate the route in the shortest possible time.

The state highway within the Manawatu Gorge is a difficult road to work on as it is narrow, is cut into the southern side of the gorge and is located 20m above the river with extreme bedrock topography, making the design and construction of foundations a technically difficult procedure. The team worked around the clock to remove slip debris, stabilise the slope and re-build the affected section of the road, all while achieving an accelerated completion date for opening to two way traffic of only four and half months from the time the final slip debris material was removed from the road shelf.

It has been noted that the delivery of the new 51m long bridge, from conception to completion, is the fastest recorded in New Zealand for a bridge of this scale to date.

The Manawatu Gorge project went through to the NZ Roading Excellence Awards and came out winning the 'Maccaferri Excellence Award for a Medium Road Project - 2013'.

"To build such a complex suite of structures in a tight natural environment is truly outstanding, and probably without comparable precedent in New Zealand. The team has really pulled out all the stops."

David McGonigal, NZTA

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