Waka Kotahi NZ Transport Agency’s project managers and consulting engineers are finalising the options for SH25A to repair the slip site at Taparahi.
The options assessment report will be completed and a preferred option announced in May.
Some initial findings have been released by Waka Kotahi.
Option one was to build a bypass around the slip. Analysis so far has shown a northern bypass option, shifting the road well away from the slip face, would need substantial digging out and removing around 300 to 400,000 cubic metres of soft soils off site before any work on building a road could start. There are other complexities to be factored in this option, including ecological impacts and lack of sites in the Coromandel to take the soil material.
A bypass closer to the slip face is another solution. It would bring a few more corners into the new road alignment and involve rebuilding an embankment with a mixture of cut into the banks above and filling over the slip below with rock fill. The old slip material – both new and historic layers – would also have to be removed and doing this task in winter would have to be factored into the programme. The design, safety and ecological impact of the proposed road re-alignment are currently being assessed.
Option two was a bridge spanning the length of the slip crater. At this stage, Waka Kotahi said, the information and advice gathered is showing a steel bridge (rather than a bridge with concrete beams) could be the fastest to construct. Time saving options such as precast deck elements and long beams that aren’t too heavy are being investigated, to reduce the number of time-consuming piles to be installed. This would also require a smaller crane to lift the beams, ideal as building a stable crane platform and access on weak soil would be time consuming.
Option three, the development of a retaining wall to re-form the road embankment, is also being investigated. Recent soil testing using cone penetrometer test equipment to better understand the ground conditions, will be key in deciding if rebuilding embankments are viable options.
THE COROMANDEL LOOP
Meanwhile, work is continuing to repair the following sections of SH25, also damaged during the summer storms.
SH25 Opoutere-McBeth underslip
Work on the permanent repair is well underway. The slip face has been stablised with a temporary rockfill and a bench has been created on which to sit the retaining wall. Work this week includes surveying the wall alignment, getting construction materials to site, creating drainage beneath the retaining wall, and the placement of facing blocks.
Two traffic management teams are currently on site looking after both daytime and night-time traffic management, and site monitoring. Light vehicles (including boat trailers and caravans) can still use the temporary diversion track. Road users should expect road closures of up to 30 minutes between 9.30am and 2.30pm on weekdays so avoid travelling at this time if you can. The road will need to be closed periodically in the coming weeks and Waka Kotahi will work with the community and freight around the timing of this.
At this point, weather permitting, works are expected to be completed and the road fully opened for both heavy and light vehicles by the end of May.
SH25A Taparahi slip
The design options are currently being prepared with final investigation works being undertaken as required on the site itself.
SH25A western side
Works to cut back the remaining slips which impact the road remain underway. The road up to the Taparahi slip is now fully open to two lanes. The cutting back of any remaining slip material has now reduced in priority and undertaken when resources have availability between higher priority sites.
SH25A eastern side
Works to cut back the remaining slips which impact the road remain underway. Major works are required immediately west (uphill) from the west-bound passing lane and are programmed to be delivered in May. The gated road closure will be moved to the Puketui Road intersection at the end of May.
SH25 between Thames and Te Kouma
Vegetation clearing, including the removal of large trunks and root balls, is underway as well as slip removal and drainage reinstatement. The construction of a major rockfill embankment between Ruamahunga Bay and Tapu started last week and is expected to be completed at the end of the first week of May. The road is open to stop/go traffic management at the rockfill site during the day and the road is fully reopened to two reduced width lanes at night.
SH25 Coromandel to Tairua
Slip removal and drainage reinstatement is underway on SH25 between Coromandel and Kuaotunu. This work will continue on a priority basis over the next couple of weeks. Geotechnical drilling works will be required through a narrow area of SH25 between Kuaotunu and Wharekaho in the second week of May. The works will require night-time full road closures – potentially up to five nights (Sunday through Thursday nights). Any closures will be advised to the public in advance.
SH25 Hikuai Settlement Road dump site
Material continues to be moved from stockpiles and slip sites on SH25 and SH5A to the clean fill site. Stop/go traffic management may be in place on Hikuai Settlement Road to allow material for the new access route to be placed on-site.
SH25 Whangamatā to Waihī
Slip removal and drainage reinstatement is underway on SH25 between Whangamatā and Waihī. This work will continue on a priority basis over the next week. Guardrail reinstatement will be completed between Whiritoa and Waihī during the next couple of weeks.
Permanent repair works on the underslip between Whiritoa and Waihī is likely to start late May/early June, weather and site conditions permitting, once the SH25 Opoutere-McBeth underslip repair has been completed. To deliver the permanent repair works the road will need to be closed periodically; any closures will be advised to the public in advance.
SH25 Manaia
Site investigations have been completed and geotech design work is underway. In the meantime the site is being monitored by Waka Kotahi and a geotech team.
