Repair and Modification of NZ Railway Tunnels

[John Ashworth]

Repair and Modification of NZ Railway Tunnels

Summary

The current NZ rail network is approximately 4000km long, with
145 tunnels ranging in length from 50m to 9km and with a total
length of 87km. The tunnels were opened between 1867 and
1980 and have been constructed in a diverse range of geological
conditions. Tunnel cross-sections and lining arrangements have
varied over the period and only two tunnels can be considered as
being modern designs.

The tunnels have performed remarkably well and the major
reasons for modifications have been invert lowering to
provide greater clearances for larger rolling stock or to permit
electrification. A few tunnels have required works to repair lining
failures due to swelling ground pressures and, in a small number
of tunnels, lining repairs have been required to remedy lining
deterioration due to a low standard initial construction.

This paper describes the philosophy and approach taken in the
repair and modification of a number of tunnels over the last 30
years.