North South Junction

Background

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. The stretch of line has five tunnels that total 920 metres and is along some of the most weather exposed on the network with the Tasman Sea and SH1 on one side and steep cliffs on the other.

The issues

Over the last 126 years this section of line has been considered unreliable and inefficient.

Because of its location the stretch was prone to slope instability which caused numerous derailments over the years. Smaller slips also caused numerous delays to freight and passenger services and the risk of slips meant a long standing speed restriction has been in place for the entire area. Of the 16 most at risk slip areas in the Wellington Region, 9 of them were along this stretch.

In addition, the tight rail alignment constructed around one particularly difficult area known as Bean Pole Corner was the cause of a derailment in 1978, that claimed the lives of two people.

Speed restrictions were also enforced in the tunnel areas because of their narrow width and height.

This resulted in a stretch of line that caused bottlenecks and inefficiencies which also constrained passenger or freight service growth.

The project

With the completion of double track on the Kapiti Coast metro area the North South Junction stretch was the last to be upgraded to increase the capacity of the line.

In 2010 we started an ambitious piece of work to upgrade the strecth and address the issues that caused delays.

The North South Junction project proposed to increase the speed of traffic through the area by:

  • Lowering four of the five tunnels to provide increased clearances
  • Stabilisation works on all critical slopes
  • Easing of curves
  • Upgrading the signalling

Over 200 workers undertook 13 shifts a week to complete the work which involved:

  • Improving the track by installing 1400m of new track using around 2000 timber sleepers
  • Upgrading the tunnels by lowering 861m of tunnel with 2000m3 of rock removed from them and pumping in half a million litres of grout into voids behind the tunnel linings
  • Increasing slope stability by installing around 1700 rock anchors in the tunnels, 300 rock anchors between the tunnels, 700 anchors on slopes adjacent to the tunnels and several hundred metres of retaining walls and rock protection fences plus 8,700m of rock fall netting. Some of this work involved workers abseiling the cliff face and helicopters dropping in rockfall netting to avoid disrupting train services.

Twenty bridges in the Wairarapa were also upgraded or repaired as a consequence of the North South Junction work as freight trains were diverted down the Wairarapa Line when the lines were closed for work during Christmas period 2010.

Construction Programme

Tunnel strengthening: August 2010 – December 2010

Tunnel lowering: December 26th 2010 – January 9th while line was closed

Slope Stability: August 2010 – May 2011

Drainage and Cabling: March 2011 – August 2011

The challenges

The work needed to be carried out with minimal disruption to services but some work would require the lines to be closed completely.

The work needed to be completed in a short time frame.

The work environment was challenging with steep and rocky hillsides and restricted working spaces in the tunnels.

Up to 20 work crews on site 24 hours a day seven days a week working with limited radio coverage and reduced visability due to dust and work noise.

Keeping safe

In order to ensure workers were safe and services could operate we implemented a comprehensive protection and communication system.

This worked by ensuring all worksites had two way communication with the nominated person in charge in spite of the constrained nature of the tunnels and site.

The system ensured all workers were aware of, and able to stay safe around, both train operations and other site work activities at all times.

Success

Safety of line improved through slope stabilisation improvements.

Speed restrictions as low as 25 kph eliminated and line speed increased to 70 kph.

Increased capacity - Faster passenger and freight services means more services can use the line. In addition the improvements allow bigger and heavier freight rolling stock through tunnels.

Over 45,000 hours of work conducted by main contractor with no lost time injuries.

Project delivered on time and to budget.

Increased reliability – the new infrastructure has achieved a reduction in service delays including a 6% improvement in on time performance and significant reducing in delays due to speed restrictions.

In conjunction with other Kapiti line improvements, freight service journey times between Wellington and Palmerston North have been improved by up 20 minutes.