KiwiRail, Wellington New Zealand
Laser profile survey tests the feasibility of tunnel modifications needed to accommodate new rolling stock on the Wellington rail network
KiwiRail (formerly ONTRACK) owns and manages New Zealand’s rail network on behalf of the New Zealand Government, maintaining 4,000 kms of railway track, bridges and tunnels.
The 10 km single track Johnsonville Line is a commuter branch line running through very steep terrain between Wellington and the northern suburb of Johnsonville. With its sharp curves, steep grade, gorge spanning bridges and seven narrow tunnels between 100 and 200 metres long, the Johnsonville Line imposes restrictions on rolling stock on the Wellington network.
Trains purchased in 1980 would not fit through the tunnels and required the retention of older trains for services on this line only. This led to escalating costs due to the need to maintain different types of rolling stock.
In establishing a business case for new trains to run on the entire network, KiwiRail needed to quickly identify if it was feasible to lower the tunnel soles on the Johnsonville Line to accommodate the proposed new trains under the Wellington Regional Rail Programme (WRRP) initiative. The concern was that if one or more of the tunnels couldn’t be modified then considerable design effort would be wasted.
Prior to the WRRP proposal, Geomatic Technologies (GT) had conducted a laser profile survey of the Wellington network for KiwiRail and supplied GT’s Asset Inspection Mapping System (GT AIMS) hardware, software, training and support. KiwiRail had intended to carry out the tunnel analysis by itself, however, other urgent work for the WRRP meant that GT was asked for assistance.
GT was able to pass the kinematic envelope for the proposed new trains through the GT AIMS recorded laser data. This highlighted a number of encroachments within the Johnsonville Line tunnels.
GT generated cross sections from consolidated laser data every 2 metres through each tunnel producing 80 cross sections for an ‘as built’ model of the tunnels.
The resulting plans gave KiwiRail the confidence that they could commit expensive design and engineering resources to the project with the knowledge that all the tunnels could be successfully modified.
A later detailed topographical survey of the Johnsonville Line confirmed the accuracy of the laser profiles and these were loaded directly into an alignment design package used to develop a final engineering design for the tunnel modifications.
– Using GT AIMS, GT was able to give KiwiRail a comprehensive understanding of the Johnsonville tunnels in a much quicker and cost effective fashion than using conventional survey teams on-site.
– Previously recorded laser data was reused for determining feasibility of tunnel modifications on the Johnsonville Line thus increasing the return on investment for the original laser survey.
– The laser data found further use as an input into the actual engineering design of the tunnel modifications, thus increasing the return on investment that KiwiRail had made in undertaking the initial laser profile survey.