A North American method for establishing an optimised slope-failure preventive maintenance programme for use by roading authorities has been identified and trialed by way of a case study, to determine its application to New Zealand roads.
The method requires a knowledge of the slope instability, and accident and maintenance history affecting the site.
This information can be used to quantify the risk to road users from adverse slope instability affects, and to identify and cost a range of preventative maintenance programmes which could be implemented to mitigate the risk.
A study was carried out in 1997–98 on a length of State HIghway 73 (Christchurch to Arthur's Pass) to verify the suitability of the method for New Zealand roads. The existing slope-failure maintenance programme at the study area, involving detritus clearing and call outs to remove rockfall material from the road, appears not to be the optimum when considered in terms of present value costs (NZ$1998), over a 25-year term. Alternative maintenance programmes would provide significant cost savings.
The methodology detailed in the research study could be used by Transit New Zealand in conjunction with its present preventive maintenance strategies to identify optimum slope failure maintenance programmes. It could also be used to provide New Zealand roading authorities with procedures for implementing an appropriate standard of care for those sites where slope stability hazards pose a safety problem.
Keywords: assessment, benefit, cost, geotechnology, hazard, instability, maintenance, New Zealand, optimisation, probability, risk, roads