To Landowners and Effected Persons of Route 52 washout at Alfredton/Tiraumea
The Tararua Alliance, on behalf of the Tararua District Council, are managing the repairs of the culvert failure and subsequent road washout on Route 52 that occurred in July 2017. Since the event we have re-established the temporary bypass road utilising the existing formed farm track to the east.
Given the depth of the failed culvert below the road, 12 vertical meters below road level, it took significant time to excavate down to the old invert level. This is evident from the scale and size of the excavation required. These efforts were hampered by adverse weather conditions throughout August and September. Design of the replacement culvert was also dependent upon removal of the old culvert as the vertical levels of virgin ground are an important part of design considerations.
Early identification of design delays, due to removal of the old pipe, led to further improvements of the temporary bypass road. Extension of the bypass culvert and road widening to accommodate heavy vehicles was completed minimising the disruption to road users, businesses and the community.
While initial design concepts included risk adverse proposals, the Tararua Alliance invested more time and effort into the design review to reduce construction costs, increase resilience and reduce the risk of failure in the future while accommodating the likely increased effects of climate change. We have eliminated the need for a drop structure, decreased the pipe diameter to a size that is far more available to supply than those first proposed, while ensuring resilient infrastructure that is fit for purpose. The replacement culvert is still twice the diameter of the old pipe, but with less flow deviations and components to block or fail in future adverse weather events.
Due to the national shortage of concrete pipes the industry is currently facing, some of the materials required for these works have be sourced from as far as Christchurch. Pipes are expected to be arriving onsite during the week starting 5 March with laying of pipes immediately following delivery.
While we intend to complete the works as quickly as possible, the onsite safety and quality of the work completed is paramount. There is a significant quantity of engineered fill to borrow, place and compact after the pipes are installed which will take some time to complete. Once this is backfilled to the appropriate level, a new road base and alignment will be constructed and sealed. There is around 23,000m3 of material to fill. These works are expected to take several months to complete.
The Tararua Alliance would like to thank the communities of Tiraumea, Alfredton and the surrounding areas for their patience and understanding while we remedy this issue. Scott McIntyre (phone: 027 801 6404) is our Construction Supervisor who will be the contact for these works until completion of the project before July 2018.