North South Junction, Wellington

Date: December 2010

Client: Downers/KiwiRail

Consultant: Novare Design

Contractor: Calder Stewart Industries Limited

Constructed in the 1880s, North South junction is a 3.1km section of single track between Pukerua Bay and Paekakariki on the North Island Main Trunk Line.  This stretch of line has five tunnels that totals 920m.

Due to the narrow width of the tunnels and limited height clearance, this section of line was considered unreliable and inefficient.  Speed restrictions as low as 25kph had to be enforced in the tunnels to minimise the risk of derailment or accidents.

In August 2010, Downer was awarded a contract to carry out lowering four of the five tunnels, including stabilisation works on all critical slopes in between the tunnels.  As part of the project BBR Contech was awarded a subcontract to carry out contact grouting behind tunnel linings and installation of rock bolts to tie back the tunnel walls.

Approximately 500 cubic metres of contact grout was pumped behind the brick lining and 1,700 rock anchors installed.

Some of the challenges included short time frame for work to be completed, confined work environment, working on live lines with minimal disruption to rail services and dealing with difficult ground conditions on site.

The work had to be carried out in shifts with crews on site 24 hours a day, seven days a week.

Despite all the challenges, the project was delivered on time and within budget.