Kaikoura SH1 Rockfall/ Shallow Slips Protection

Kaikoura is a coastal town, north of the Canterbury region of the South Island of New Zealand. It is a popular tourist destination known for its abundant wildlife and Sperm Whale population. The region was badly affected by an earthquake on November 2016. The magnitude 7.8(Mw) earthquake caused landslides and rockfall along the coastal road of State Highway, SH1. The state highway links the town north of Kaikoura to Blenheim and south to Christchurch and at the same time serves as a major tourist route with its scenic view along the coast. Rail corridor also sits along the side of the SH1 responsible as a major transportation mode to bring goods in from Picton.

Not long after the earthquake, the government set up the North Canterbury Transport Infrastructure Recovery (NCTIR) - an alliance between the NZTA, KiwiRail and major contractors and engineering consultants. NCTIR is tasked to restore the transport infrastructure networks within a given time frame to pre-earthquake condition.

One of the major restoration works among many that the NCTIR team has to cope with is known as Site SR32.

The landslide caused by the slope above the road and rail tunnels have inundated the entire road. While loose surface rocks and debris have been cleared as much as possible, the residual risk will be mitigated by installing ETAG energy certified fences at some distance above road level near to the road and rail tunnel entrances.

The NCTIR team has identified a minimum kinetic energy capacity of 2000kJ fence manufactured by Maccaferri - RMC200A for this location. Specialist contractor - Rock Control Ltd was assigned to carry out this very challenging job site. There are 3 fences in total for this site, all 4m high posts with section length ranging from 40m, 50m and 60m designed to protect the road and rail below in another rock fall or shallow landslide event. They are all installed on the slope profile above the road level. Not long after the fence installation before the road reopened, one of the fences was hit by a shallow landslide with an estimated volume of approximately 15 m³ and successfully arrested. The impact energy didn’t cause any significant damage to the fence and this debris was later cleared by the contractor.

Geofabrics New Zealand supply the full range of Maccaferri ETAG027 energy certified rockfall fences starting from 100kJ to 8,500kJ. The intercepting component (panels, posts, base plates, upper and lower ropes, energy dissipaters, up-slope and lateral ropes) used in the rockfall fence are fully tested against impact under the stringent ETAG 027 test procedure.

The performance of the fence along with the measurements are used to calculate the maximum energy rating and are recorded after which a certificate is issued stating their energy level among others. Up slope and lateral anchor loading requirements are provided to the engineer for the anchor design.

A certified rockfall fences/system significantly reduces uncertainty in the energy capacity of a rockfall protection structure designed by the engineer. The engineer can then put more attention on the design of the remaining component below ground i.e anchors and foundation element.

The Maccaferri rockfall fences are now available in the latest trajectory analysis software - Rockfall produced by Rocscience for modelling purposes.

Impact Performance of the RMC200 Fence

On 20th Feb 2018, the Kaikoura region were badly affected by Cyclone Gita. This has resulted in further landslides along the coastal transport corridor. Site 32 was not exempted from the damage done by Cyclone Gita where an estimation of 200 tons of rocks and saturated soil debris collapsed from the upper slope source area. The entire volume of debris impacted one of the fences and was successfully arrested by the fence. The fence was originally designed for rockfall impact but in this instance the fence has demonstrated its ability to intersect a shallow land slips or debris flow situation.

The debris was later remove by the specialist contractor - Rock Control Ltd and the fence reconstructed to meet its intended function for another potential impact to protect the rail and road infrastructure.

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Kaikoura Rockfall / Shallow Slips Protection Case Study

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