This contract was for the Far North District council and involved construction of a steel and timber footbridge and cycleway bridge cantilevered off an existing rail bridge which services the vintage railway train. The bridge spans a total distance of 33.4m over the Tirohanga Stream. The work included replacement of existing pile crosshead, new driven timber piles at the piers and abutments, supply and installation of steel beams and bracing and construction of a 1.5 m wide cycleway including handrails.
The main challenge involved with this project was working on a live rail track with trains passing most days. We established a working relationship with the vintage railway whereby we had a schedule of the train movements and they contacted us prior to each movement to ensure we were clear and it was safe to proceed. We were also working over a river which flooded a couple of times during the work’s period which sent debris down through the work site.
Another challenge for the project was the requirement for changes to the design during construction as the initial design didn’t allow for building a straight cycleway onto a slightly curved and cambered existing rail bridge (design assumed the rail bridge was straight and level). This meant there were changes to the approaches of the cycleway, changes to the steel work and fixings. The approaches to the bridge also needed to be modified as the design did not take into account for the heritage trees near the cycling access on one side of the bridge. The approaches required some earthworks on the grades of the approaches to ensure they complied with cycleway standards. This was all managed through the engineer and we managed to keep the original tendered sum due to the variations being kept below the total of the provisional sums included.
Our key innovation for the project was to use larger piling equipment than would typically be used for the piles we were installing as this allowed us to install the piles from each side of the riverbank without the requirement for temporary staging or entering the river. Our 35T piling crane was able to reach out and install the piles on the central pier which would not have been achievable with other equipment.