SH6 Dellows Bluff – Rockfall mitigations works

In response to a rockfall event triggered by heavy rain, Abseil Access undertook initial investigation works and collaborated with WSP to develop a rockfall mitigation strategy for a bluff. This comprehensive project included a geotechnical investigation of sandstone above a mudstone cliff, scaling of loose material, and removing 188 cubic meters of rock through drilling and blasting to reshape overhanging features, reducing the need for extensive rock bolting. The strategy also involved “pull out” testing to measure rock capacity up to 660kN, installation of 280 six-meter rock bolts to secure two sandstone bands, and anchor acceptance testing for 10% of production anchors.

During the project, Abseil Access implemented blast plans to cut the sandstone bands with minimal back breaks, scheduling blasting during limited two-hour evening road closures to minimise traffic disruption. Additionally, due to the risk of rockfall at the construction level, all materials were helicopter-lifted to the site, and two suspended drill rigs were used to drill 1,680 meters for anchoring, ensuring efficient project progression.

Scope of Works:
  • Geotech investigation of sandstone features above mudstone cliff
  • Scaling of loose material
  • Removal of 188m3 of rock using drilling and blasting to reduce number of rock bolts required
  • "Pull out" investigation testing of rock capacity up to 660kN
  • 280x 6m rock bolts installed to secure two sandstone bands
  • Anchor acceptance testing of 10% production anchors

Challenges and Solutions:

The project presented unique challenges due to the complex nature of the terrain and the need to ensure minimal disruption to road users. Innovative blasting techniques, scheduling, and aerial transport of materials were critical in overcoming these challenges while maintaining safety and efficiency.

Outcome:

This project successfully enhanced the stability of Dellows Bluff, significantly reducing the risk of rockfall events along this crucial section of SH6. The collaboration between Abseil Access and WSP and the use of advanced techniques ensured the project’s success within the stipulated timeframe, contributing to safer travel for road users in the region.

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