The rejuvenation of the Makatote railway viaduct has been shortlisted for The Structural Awards 2017. The project provided a magnificent historic structure with a new lease of life that will take it well into the 21st century. Institution Fellow, Sulo Shanmuganathan, explains the unique challenges faced by her team and the remarkable solutions they provided.

This remarkable viaduct’s fine lattice steel structure had suffered from the ravages of time and the demands of modern trains, leaving its future in doubt – though when approached by KiwiRail to assess a solution, we were convinced the viaduct should be given a new lease of life: it is a unique piece of New Zealand’s engineering heritage, an elegant assembly of tall, slender steel towers and lattice girders that is considered one of the last remaining major structures designed by New Zealand’s renowned Engineer, Peter Seton Hay (1852 – 1907).

The project would be challenging, particularly in terms of providing access and temporary supports for the painting and strengthening works that were required. The viaduct is 80m high from the stream, located in a gorge with vertical cliffs, and there is not adequate access to bring heavy construction machinery – so it would be difficult to construct the temporary access towers and platforms necessary.

We chose to use the viaduct’s steel structure and concrete foundations to support the towers and platforms, carefully planning a series of construction sequences (so as not to overload the structure) and working around the normal timetable of train operations. This meant that every day’s activity required precise unique planning.

When restoring a heritage structure of this size and beauty, one needs to be mindful of the existing form, fabric and appearance. It also goes without saying that the look and feel of the structure should not be changed. Consequently, one needs to work within hidden spaces to provide the new members and strengthening systems to make the structure look the same after the strengthening.

Over 15,000m² (about the area of two football pitches) of old lead paint were carefully removed and vacuumed away to avoid contaminating the rich natural environment below which was home to nesting Whio (an endangered Kiwi duck). This involved the provision of encapsulated work spaces: where parts of the structure were isolated and sealed with plastic sheathing so that they could be blasted and cleaned and without damaging the sensitive local environment. 

The surfaces were then repainted with an advanced paint to last another 50 years. The lattice steel structure was subtly and skilfully restored and enhanced, increasing the load capacity by 25% to accommodate new, heavier trains. There is virtually no visual clue to the strengthening regime and the elegant clean lines of the original structure are completely unspoilt.

In all, the project represents a triumph of engineering-led conservation that leaves the vision of 19th and early 20th century railway men unspoilt for 21st century generations to enjoy.

Our client, KiwiRail, are delighted with the work – they now have a structure with a new lease of life for another 50 years or more. Ms Alison Dangerfield (Heritage Advisor Architecture, Heritage New Zealand) commented: 
“The Makatote Viaduct refurbishment programme has been consistent with its outstanding heritage values and vital for the future wellbeing of the viaduct. It remains essentially unchanged - a dramatic structure of great achievement.” 

Makatote Viaduct

Read more in The Structural Engineer or Explore The Structural Awards shortlist.

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