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. Immediate response included heli-sluicing and scaling, while the long-term solutions included permanent slope remediation designs to mitigate against future failures.
The damage to Ohau Point, approximately 180m high from sea level, was the main impediment to re-opening the road north of Kaikoura. With the upper 60m of the slope subject to ongoing rockfall and shallow instability, the slope needed to be remediated before access could be granted to the road construction team below the rock face. GeoStabilization was awarded the project through a competitive tender process with our strong attributes and extensive experience in rockfall.
The conforming solution included a pattern rock bolting and dimensioned high tensile steel wire mesh stabilisation system. Using Geobrugg’s high tensile steel wire TECCO® mesh and our proprietary T40 low-carbon steel hollow bar anchors with 2m vertical and horizontal spacing, the 6,000 m2 dimensioned rockfall solution provided a 100-year design life protecting against shallow failures.
During the early stages of construction, it was found the slope was in much worse condition than originally anticipated and a revised design was required to accelerate the construction programme. GeoStabilization proposed a number of alternative design build solutions with a ring net drape option being preferred by the Client (NCTIR). This solution involved the installation of 6,000 m2 of high tensile 6 on1 steel wire ring net prior to installing the TECCO® mesh. Once the ring net and TECCO® mesh were installed the drape was closed off across the bottom using three 22 mm diameter steel wire ropes.
Immediately following the installation of the drape, the lower slope (a further 12,000 m2 of subvertical rockface) was scaled by GeoStabilization’s rope access technicians to make the slopes safe for the road construction teams to rebuild the highway. The pattern bolting was then completed drilling through the drape.
Following a series of sub-tropical rainstorm events, Kawakawa 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.