The New Zealand Railways Magazine, Volume 4, Issue 5 (September 1, 1929)
The Ngaruawahia Bridge
The Ngaruawahia Bridge.
The Ngaruawahia bridge carries the Main Trunk line over the Waikato River at Ngaruawahia, near Frankton. The existing bridge (timber and iron with cast iron cylinder piers) was built about the year 1876. Practically all the original native timber have since been replaced with ironbark in the course of maintenance, and much of the ironwork has also been replaced or strengthened. Present-day engine loadings now far exceed those of former days, however. Therefore, the old bridge, with its materials rapidly deteriorating in spite of careful maintenance, has now reached the end of its useful life.
The new bridge will have three 120ft. spans and three short approach spans. The main shore piers will be of mass concrete resting on piles, and the river piers will be reinforced concrete cylinders, ten feet in diameter at the base, sunk to a depth of about 40 feet below water level. At both Ngaruawahia and Whenuakura bridge sites, borings have been put down near each new foundation, and test piles driven and loaded with test loads in order to determine as far as possible the conditions to be met with in constructing the foundations.