Rockfall Mitigation and Slope Stabilisation for an Earthquake-Damaged, Cliffside Road in New Zealand

Project Info

Christchurch City Council (project jointly funded by Christchurch City Council and NZ Transport Agency)

Christchurch, New Zealand


In 2010 and 2011 a series of earthquakes caused major damage in and around Christchurch, New Zealand. Sumner Road is an important link between Christchurch, the Port of Lyttleton, the communities of Sumner and Lyttelton, and is also a popular scenic tourist drive. It was very badly damaged in the earthquakes by thousands of cubic metres of rock falling onto the road from the steep slopes above. Sections of the road were also severely damaged by failed retaining walls. The road needed to be rebuilt, and rugged bluffs above required stabilising to reduce the risk of further rockfalls.

Following the earthquakes, Golder was appointed to a specialist slope stability engineering panel by Christchurch City Council to help address earthquake induced damage around Port Hills. Repair of Sumner Road between Evans Pass and Lyttelton was the biggest and most difficult project led by the Council. It involved designing and implementing rockfall protection along a 2 km stretch of the heavily damaged road, flanked by cliffs as high as 150 metres.

Partnering with a number of local subcontractors, we developed the preliminary design for mitigation measures in the complex terrain with unique biodiversity values. We also acted as owner’s engineering advisor for the Council with presence onsite throughout the 2.5 year construction period of this logistically challenging project.

The rockfall mitigation works involved scaling and blasting of loose rock from the massive rock faces above the road, and construction of a wide catch-bench to reduce the risk of future rockfalls on the road. With the rockfall mitigation complete, the project extended into repair of 30 earthquake-damaged retaining walls and the road itself.

Drones and other measures were used throughout the project to monitor rockfall activity in specific areas, reducing the need of rope access by abseil teams and minimising safety risks. The use of drones will also enable more efficient monitoring of the cliffs in the future, reducing road closures.

The road reopened at the end of March 2019, to the satisfaction of the Christchurch City Council and the celebration of communities in Sumner and Lyttelton, who have been eager to see the road reopen, tourists return to the area, and pressure reduce on the Lyttelton road tunnel.

Our expertise has been instrumental in the safe completion of the project and the longer-term safety of road users. We’ve also helped the Council save more than NZD$15 million and have a much-reduced environmental footprint, compared to previous concepts developed for the project, due to our innovation in the design of the rockfall mitigation measures.



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