Geohazard Engineering
Ohau Point Rockfall
Post-earthquake rockfall mitigation on 180 m of near-vertical coastal cliff — the critical obstacle to reopening State Highway 1 north of Kaikōura.
- Location
- Ohau Point, SH1 north of Kaikōura
- Client
- NCTIR (North Canterbury Transport Infrastructure Recovery)
- Designer
- GSI NZ
- Timeline
- 2017 — Kaikōura earthquake response
- Scope
- 6,000 m² TECCO mesh dimensioned rockfall system plus 12,000 m² rope access scaling
Design
The Primary Obstacle to Reopening SH1
The November 2016 Kaikōura earthquake was one of the most complex seismic events in New Zealand's recorded history, triggering widespread rockfall, landslide, and debris flow damage to State Highway 1 and the main trunk rail line north and south of the town. The coastal slopes above the highway were severely destabilised, and immediate response included helicopter sluicing and scaling while permanent solutions were developed.
The damage at Ohau Point — approximately 180 m above sea level — was the primary impediment to reopening SH1 north of Kaikōura. The upper 60 m of the slope was subject to ongoing rockfall and shallow instability, and the face had to be permanently stabilised before access could be granted to the road construction teams rebuilding the highway beneath. GeoStabilization NZ was awarded the project through a competitive tender process, recognised for our experience in large-scale rockfall mitigation and rope access capability.
The conforming design specified pattern rock bolting and a dimensioned high-tensile steel wire mesh stabilisation system using Geobrugg TECCO mesh and proprietary low-carbon steel hollow bar anchors at 2 m vertical and horizontal spacing — a 100-year design life system providing protection against shallow failures across 6,000 m².
Build
Worse Than Expected — Design Rebuilt on Site
During the early construction stages, it became clear the slope was in significantly worse condition than originally assessed. Ongoing instability and the risk of collapse during installation required a revised approach to accelerate the programme and improve safety for the installation crews.
GeoStabilization NZ proposed a number of design-build alternatives. The preferred option was a ring net drape system — 6,000 m² of high-tensile 6-on-1 steel wire ring net was installed across the slope prior to the TECCO mesh, providing immediate containment of the unstable face material. The bottom of the drape was closed off across the full width using three 22 mm diameter steel wire ropes, retaining material behind the system while the lower slope was made safe.
Immediately following the drape installation, GeoStabilization NZ's IRATA rope access technicians scaled 12,000 m² of near-vertical sub-vertical rock face below — making the lower slopes safe for the road construction teams rebuilding SH1 beneath. Pattern rock bolting was then completed by drilling through the installed drape.
Deliver
18,000 M². SH1 Reopened.
The completed works covered 18,000 m² of coastal rock face — 6,000 m² of dimensioned TECCO mesh rockfall protection system, combined with 12,000 m² of rope access scaling to clear the lower face. The installed system provides permanent 100-year protection against shallow rockfall from the upper slope, with the ring net drape providing an additional containment layer for any future movement.
Ohau Point was the critical constraint on reopening State Highway 1 north of Kaikōura. The project required rapid design adaptation in response to conditions encountered on site, simultaneous management of an active rockfall hazard, and rope access operations on a near-vertical coastal face while road construction teams worked below. It remains one of the most demanding large-scale rockfall mitigation projects completed in New Zealand.
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