After the slip occurred, Tauranga City Council asked an engineering consultancy to analyse the slip site and suggest repair options, with cost estimates. Tauranga City Council initially chose to proceed with a significant realignment of the base track along the coastal margin, involving a new 360 metre long section of track included extensive rock revetment and boardwalk sections. After securing resource consents and completing detailed design, Tauranga City Council abandoned the proposed solution as the construction cost (around $5.5M) significantly exceeded the available budget.
In October, newly elected Mayor Tenby Powell made a pledge that the original alignment of the base track would re-open by Christmas 2019 and called us. The main project challenges were the proposed design solution had to be robust and delivered in a five-week timeframe in a location that has significant access restraints. The Mauao Base Track is of significant archaeological importance and has two Pohutukawa trees that could not be damaged.
OUR APPROACH
The only way to have achieved this was through complete collaboration with everyone – the Trustees of Mauao, Tauranga City Council staff and elected members, Heritage New Zealand, the contractor and arboriculturalist. Everyone was onboard and committed to seeing the base track open. We achieved consensus through a series of onsite meetings and a Risk Workshop. As part of our commission we presented four design options for consultation, along with 3D visualisations of the proposals which was instrumental in getting swift sign off by the Trustees and Heritage New Zealand.
OUR SOLUTION
The preferred solution involved retreating the track slightly in to the hill, avoiding the Pohutukawa trees and then installing soil nails and horizontal bored drains in to the new slope above the track, along with the existing slip face below. Following this a new fence was installed.
OUTCOME/CLIENT BENEFITS
We ensured Tauranga City Council and Mayor Tenby Powell delivered on the promise to have the track reopened in time for Christmas.
KEY FACTS
Nearly one million people are believed to walk up or around Mauao every year. Mauao historic reserve is owned by local iwi Ngai Te Rangi, Ngāti Ranginui and Ngāti Pukenga in the form of the Mauao Trust. The reserve is managed jointly by the Mauao Trust and Tauranga City Council under the direction of the Ngā Poutiriao ō Mauao.
