This project involved the design and installation of a 180 m‑long with post bases 30 m above road level, rockfall attenuator fence, one of the longest installations of its kind in New Zealand. Constructed on a steep rockfall-prone slope above State Highway 6, the works were undertaken in a live traffic environment with complex access, geological and logistical constraints.
O’Sullivan’s Attenuator Fence – One of NZ’s Longest Rockfall Attenuator Installations
Key Challenges
- Steep, weather exposed coastal terrain
- Fractured geology and subsurface voids encountered during drilling
- Requirement to maintain at least one live traffic lane at all times
- Limited upper slope access, requiring extensive helicopter logistics
- Large scale installation at height using rope access techniques
Scope of Works
- Scaling and blasting of unstable rock
- Drilling and installation of 209 anchors, including production bolts, attenuator anchors, base anchors and investigation bolts
- Total drilling of 1020 linear metres, with a maximum daily output of 51 m drilled in a single shift
- Installation of approximately 6,300 m² of Tecco G65/3 high tensile rockfall mesh
- Installation of 1.6 km of wire rope for bracing, tie backs and longitudinal cables
- Installation of 180 m of ATT 30 attenuator barrier, supported by 18 structural posts and foundations
Workforce & Programme
Notable productivity milestones included the installation of 9 anchors totalling 51m in a single shift and the placement of 12 rolls of mesh (approximately 1,400 m²) in one day.
- 22–25 personnel engaged over the project lifecycle
- Typical daily crew of 6–7 workers, with peak days reaching 8 personnel on site
- Project duration of approximately 5.5 months (October 2025 – March 2026)
Access & Equipment
- Rope access for drilling, mesh installation and anchoring
- Wagon drill rigs and a 30 m EWP for targeted access
- 60 tonne crane for fence installation
- Helicopter lifts for drill rigs, mesh rolls, anchor bars and grout equipment due to limited road access
Outcome
Despite fractured rock, geological voids, wind exposure and live traffic below, all systems were installed, tested and accepted. The completed attenuator fence provides robust, long‑term protection from rockfall events, enhancing safety and network resilience along State Highway 6.
Want to Know More? Contact Us Below:
default
default
default
default
