A programme of works to repair the 15 significant slips along SH1 Mangamuka Gorge has now been established, following investigations, planning and design work to understand the damage and plan for how we will repair this challenging transport corridor.
The road is scheduled to open and be fully operational by May 2024 however Waka Kotahi NZ Transport Agency is actively investigating opportunities to provide limited access to light vehicles over the Christmas period to connect whānau, road users, and communities on either side of the gorge.
Norman Collier, Project Director Waka Kotahi acknowledges the impact that the sustained closure is having on travel for work, school, business, and connectivity and the prospect of having the gorge closed for an even longer period of time will be disappointing for the community.
“We know how critical this route is for the community and we are continuing to investigate if it is possible to make more resources available to accelerate this work.
Northland’s ground conditions (including through the Maungataniwha Ranges which surround SH1 Mangamuka Gorge) have always been fragile and almost 70% of the geological material which forms rocks in the region are made up of Northland Allochthon.
This type of material has long been challenging for construction and maintenance of roads and means repairs to slips of this nature need to be carefully planned, as finding competent material to anchor the road to can be difficult.
“One of the most significant slips on the southern end of the gorge requires the most complex fix and will take approximately eight months to complete. There are 14 other slips which require a similar approach and will average 5-6 months construction time each.
“It has been a complex process to understand firstly the damage which occurred and then investigate and plan the best way to fix each slip. We’ll also be making the ground less susceptible to slips by improving the drainage through the gorge, so it’s more suitably equipped to handle the increase in severity and frequency of weather events” says Mr Collier.
Crews are now focused on ensuring the road is safe and stable enough to accommodate the large machinery needed to carry out slip repairs. This includes installing almost 700 piles throughout the gorge, stabilising the road and retaining and strengthening areas.
“Our teams are working in a very constrained environment, within an already tight road corridor which is made even tighter with the slips impacting the road, large machinery and multiple work sites.
“We want to ensure we get these slip repairs right while also looking after the health and safety of our teams on the ground and protecting the environment we are working in. We know the community joins us in this sentiment and we thank them for their understanding” says Mr Collier.
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