Following a series of sub-tropical rainstorm events, Waiheke and the wider Auckland region suffered extensive landslip issues. Many roads in the region developed both underslips and overslips, severely affecting the flow of traffic. On some roads, full closures were required. Having worked with our company previously on similar issues, Downer NZ contacted us to provide a competitive design/build solution for the underslip on Waiheke Road.
Working closely with the Downer engineers to ensure a suitable outcome for Auckland Transport (the client), our engineers designed a robust solution with cost, programme, and the local community in mind. As an emergency situation, GeoStabilization’s engineers conducted a site visit to determine the site’s parameters and conditions. Combined with investigation data provided by Downers, a simple solution of soil nails and shotcrete was developed to stabilise the slope and rebuild the pavement width.
SLIDE modelling indicated three rows of soil nails were required to provide a suitable factor of safety. The use of GeoStabilization’s proprietary low-carbon steel hollow bar provided the required durability. Sacrificial soil nails were tested to failure to give us a full understanding of the grout/ground bond capacity. This in-house design/build solution provided savings to the client in the order of 30% over traditional retaining systems.
After the Kaikoura earthquake in November 2016, the steep coastal slopes north and south of the town were severely affected by rockfall, landslide, and debris flow issues.