In early 2017, a sub-tropical cyclone ravaged the Far North and Coromandel regions of New Zealand’s North Island. Main roads were affected by under- and over-slips, closing many strategic routes. Houses were swept down hillsides and properties severely affected. In Onemana, the intense rain saturated a steep slope behind several properties. Eventually, the slope failed which created a shallow landslide in the order of 300-400m3 in volume. The landslide swept a small building and cars off the side of the hill, leaving one vehicle 3m up in a tree. Nearby residents were evacuated until a solution could be developed to protect the properties from future failures.
We were invited by Ormiston Associates to design the permanent solution. Following a site visit, geotechnical mapping, and a full 3D drone survey, the slope was modelled to assess the likelihood and severity of any future potential failures. The final design consisted of a 35m long 3.5m high Geobrugg SL-150 shallow landslide barrier. The system required both lateral and upslope anchors to support the structure, as well as robust reinforced concrete foundations for the posts. A total of seven posts were required to support the SPIDER® mesh panels.
The drilling was undertaken using one of our SuperNailer™ drills, with a small 10-tonne excavator used to assist in the barrier construction. A 300m2 dimensioned TECCO® mesh system was also constructed using rope-access techniques.
After the Kaikoura earthquake in November 2016, the steep coastal slopes above the main State Highway (SH1), and the main trunk rail line, north and south of the town were severely affected by rockfall, landslide, and debris flow issues.