Authors: Avery, MB; Bourke, S

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Avery, MB & Bourke, S 2013, '2011 Manawatu Gorge landslide-technical challenges faced during remediation', in PM Dight (ed.), Slope Stability 2013: Proceedings of the 2013 International Symposium on Slope Stability in Open Pit Mining and Civil Engineering, Australian Centre for Geomechanics, Perth, pp. 911-920,

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The August 2011 Manawatu Gorge landslide had an initial failure of approximately 20,000 m3. The sheer volume of the failure caused the closure of State Highway 3 through the gorge and a rapid response team consisting of consulting engineering geologists and specialist contractors acted promptly to ascertain the extent, cause and short term remediation works to allow reopening of the very important transport link. In the following months several further failures occurred which led to the development and design of extensive long term remedial works. A design workshop was held in November where scientists, engineers and specialist contractors convened to discuss options for the long term remediation of the slip. The final design included the removal of some 370,000 m3. The extent of the earthworks was determined using the Digital Terrain Model (DTM) developed earlier in the project, based on a combination of Geological and Nuclear Sciences (GNS) produced 3D laser scans and recently flown LiDAR. The earthworks began in December 2011 and finished (down to road level) in May 2012. Once excavation was completed the highway required an almost complete rebuild as there were a number of half and full bridge structures that were extensively damaged during the event, likely both from the sudden impact energy of material during failures and also the long term effects from thousands of tons of material loading the structures over an extended 12 month period. Stabilisation and drilling work on site included the installation of mesh drape, horizontal shallow inclined drainage holes, stabilisation of colluvium slopes using rock dowels and installation of a 500 kJ Geobrugg rockfall attenuator. The stabilisation of the landslide and the rebuilding of the highway structures was completed in October 2012.

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Robson, C. (2011) Site topographic map August/September 2011 (Figure 3) and general project correspondence. MWH Ltd Wellington.
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