A4 Landslide risk management for mountain roads

Abstract

When the design, construction and maintenance of mountain roads are required to accommodate landslides and difficult ground conditions, decisions need to be made based on the assessment of risk. Risk management requires a balance to be struck between acceptable risk of blockage, damage or loss and affordable cost of risk reduction. However, before these decisions can be made, an assessment of landslide susceptibility and hazard is usually required. These terms are often used synonymously in the published literature, and consequently there is sometimes some confusion in how they apply. As far as this book is concerned, the hazard and risk definitions originally proposed by Varnes (1984) and more recently elaborated upon in publications such as those of the Australian Geomechanics Society (2000, 2007), Hearn & Griffiths (2001), Lee & Jones (2004) and Fell et al. (2008) are followed. Landslide susceptibility, hazard and risk mapping techniques are discussed in Section B2.6. Landslide susceptibility refers to the potential for a given slope to fail compared to others, and the term is usually used in the context of the opportunity for first-time failures to occur. If a factor of safety (Section C3.2) could be calculated, then it would be this value that would determine the absolute susceptibility of each slope. This information is usually unavailable, however, and relative susceptibility is normally assessed by reference to conditioning and triggering factors (Table A3.2) either on a site-by-site judgemental basis or by using a formal mapping approach (Section B2.6). Landslide hazard defines the potential posed by an existing or future landslide to cause damage or loss (economic and societal). Hazard combines components of failure volume and speed of movement (sometimes referred to collectively as landslide intensity, see Hungr 1997; Australian Geomechanics Society 2007) and frequency of movement, or probability over a given area …