Dynamic Barriers
2020
SH94 MILFORD ROAD - FIORDLAND - New Zealand
Milford Road Alliance (MRA)
EAST GATE SLIP ROCKFALL PROTECTION SOLUTION
Tree trunk intercepted by barrier
Problem
Fiordland in the lower South Island of New Zealand is a very high rainfall intensity area with high occurrence of landslide and rockfall hazards. The area is surrounded by its mountainous terrain and stunning landscape. Located in the region is Milford Sound, a world- renowned tourist attraction which has attracted thousands of tourists to the area every year. SH94 Milford Road is the only route for tourists travelling in and out of the tourist destination from a nearby town – Te Anau. One of the sites along Milford Road that has been impacted by rockfall and shallow landslides over the past decades is known as ‘East Gate Slip’, 87 km North of Te Anau. Historical data maintained and recorded by the MRA suggest that most of the rock sizes fallen over the years range between 0.2 m up to a maximum of 1.0 m in diameter.
Solution
The final decision was to install Maccaferri 2,000kJ certified fence – some distance from the road level to intercept any rock fall and moderate level of shallow landslide. The fence is designed to withstand impact from rock size between 0.5m to 1.0 m in diameter with multiple impact scenarios, bringing the assessed risk levels to an acceptable level. The following potential issues were considered when deciding the suitability of solution: the ability to mitigate the range of identified hazards, necessity for road closure, cost considerations and constructability; The fence option offered was the most suitable for the site and balances each requirement. The solution meets adequate safety requirements for the site and reduce the risk to road users to an acceptable level. The entire process of installing the 4.0m (height) x 50.0m (length) fence took three weeks to complete. Soon after completion, the fence was impacted by fallen tree trunks of diameter ranging from 400mm to 500mm which was successfully stopped by the fence with marginal activation of the energy dissipator, no replacement of any fence components was required as the impact energy was minor.