Management of slope instability hazards, north to south junction, NIMT, New Zealand

The Pukerua Bay to Paekakariki section of the North Island Main Trunk (NIMT) includes a 3.4km stretch of single line between North and South Junctions which has a steep grade, many tight radius curves and five tunnels. Slopes between the tunnels are up to several hundred metres in height and are inclined at between 40° and 55°. The North - South Junction section of the line was constructed in the mid to late 1880’s and currently has approximately 50 passenger and freight movements per day. Since completion, and continuing up until the mid 1990’s, there have been a series of large failures from the slopes above the line. These have lead to track outage, occasional train derailment and a number of fatalities. In this period, risk management practices were entirely reactive, and involved either placing speed restrictions, or construction of rockfall catch fences. In the mid 1990’s, a program of pest and stock control and revegetation was initiated. In the approximately 15 year period since, the frequency of rockfall incidents have significantly decreased and there have been no large scale failures within the last eight years. However, there are still a number of areas where shallow debris/rock falls are continuing to occur, which present a significant risk to the railway line. KiwiRail are currently investigating options to improve capacity between North and South Junction. Part of this improvement will involve improving permanent speed restrictions which have been historically emplaced. This paper outlines the geological setting and history of slope failure between North and South Junctions. Additionally, the paper outlines the slope risk rating system that has been recently developed to allow a proactive system of slope risk management. Finally, the paper discusses the risk reduction works that are proposed to reduce the current slope instability risk and improve the current line speed.

Media Info

  • Pagination: 9p.
  • Monograph Title: Rejuvenation and renaissance: CORE 2010: conference on railway engineering, 12-15 September 2010, Wellington, New Zealand

Subject/Index Terms

Filing Info

  • Accession Number: 01517088
  • Record Type: Publication
  • Source Agency: ARRB
  • Files: ATRI
  • Created Date: Mar 4 2014 8:07PM