Sunday, 7 June 2015

Dunedin-Mosgiel Railway Duplication: Brief Synopsis

This was a major project that occupied some 8 years from 1906-1914. It entailed that the original line had to be kept in operation throughout. I will update this article with more information as time goes on and I do more reading but between Dunedin and Caversham this appears to be the construction methods used:
  • The new line was built on a separate alignment but directly alongside the existing line, all the way from Dunedin to Wilkie Road. This was because new bridges had to be built at Andersons Bay Road, King Edward Street and Wilkie Road. The means adopted was to make these as temporary bridges until such time as the new line could become the running line. The permanent bridges had to wait until the original line was taken out of use, which suggests they ended up cutting into the old formation. Nevertheless photos do exist showing old and new lines side by side but the old line must have been impassable by the time the permanent bridges were completed.
  • The embankment was formed from trestling that was filled in with spoil tipped from railway wagons, a common semi-mechanised method of constructing large railway embankments at that time. It contrasts with the use of pick and shovel and horse drawn vehicles used in other railway projects in NZ where a locomotive was not available to help with the work.
  • The original line was on the north or west side of the new embankment.
  • Past Wilkie Road to South Road, there was already a bridge over South Road for the existing line so the embankment was widened to take two tracks and the second track laid on the north or west side. There must have then been a second bridge provided for the new track.
  • Heading into Caversham the new station was in a different place and at a lower level, so there was a divergence from the old line again, probably just past the bridge over South Road. The new line was placed into a cutting as it approached the new tunnel at Caversham, and a number of bridges were built to take the various local streets as well as South Road over the cutting. This bridge which is a large steel structure on a big skew, was bypassed by the motorway construction in the 1980s and remains at the end of Caversham Place, just south of the tunnel portal.
  • The tunnel construction was started at the very beginning of the project, because the fill from the approach cutting and the tunnel itself were used to build up the embankment from Dunedin to Caversham.
  • Motorway construction in the 1980s resulted in big changes with essentially the pre-1914 route and part of the duplication route through Caversham taken over for the road. The railway at that time was singled and diverted, with a new embankment built from just past Wilkie Road behind Carisbrook Stadium, to the site of Caversham Station, incorporating a new bridge over South Road. South Road was diverted onto the overbridge at Barnes Drive leaving the old overbridge as a dead end, with the stub road renamed Caversham Place. Caversham itself was cut in half by the motorway and four overbridges just south of Barnes Drive were removed. The overbridge at Goodall St remains for access to the footbridge over the motorway itself. There have been further changes since with the doubling of the highway in the last few years.
  • The only remnant to be found of the old construction through the area is the old tunnel. The approach cutting has a footbridge over it at Lindsay Road giving a view down into the tunnel portal. The portal at the other end is currently fenced off.