Introduction

Design, construction and maintenance of civil infrastructure in mountainous permafrost terrain is an engineering challenge. The difficulties encountered are mainly governed by the fact that the ground is frozen and contains ice, top soil layers thaw during the warm summer months, steep and potentially unstable slopes prevail, the ground is covered with snow for long periods of the year and access can be complicated. The tendency of ground ice to creep, accrete, segregate layers and thaw causes most uncertainty when designing infrastructure. Specially adapted site investigation, construction, maintenance and monitoring techniques are required in this environment to ensure the longevity and the sustainability of the infrastructure. In addition to the potential impact caused by the presence of infrastructure, climate change is influencing air temperatures, precipitation regimes, snow cover distributions, active layer thicknesses and lower limits of permafrost occurrence in mountains (Clague, 2008; Haeberli and Beniston, 1998; Harris et al., 2009; Harris et al., 2001a). The rate and magnitude of these changes, which influence the physical, hence mechanical, properties of the ground more or less directly, and consequently the stability and safety of structures, are difficult to predict but must be taken into account in the design of infrastructure (Hayley and Horne, 2008; Instanes, 2005; U.S. Arctic Research Commission Permafrost Task Force, 2003).

The general term 'mountain infrastructure' used in this chapter refers to structures with foundations (e.g. buildings, pylons for power lines or cable cars and defence structures), roads and railways, dams (e.g. hydroelectric, avalanche and rock fall retention), water pipes (e.g. sewage pipes), underground access tunnels, ski runs and technical snow production systems. Mountain infrastructure is either located in/on frozen bedrock (containing ice in pores and fissures) or debris accumulations such as scree slopes, moraines or rock glaciers (all containing varying amounts of ice). In contrast to arctic regions, where infrastructure in permafrost includes entire communities (e.g. Instanes, 2005), there are generally no large permanently inhabited settlements in the permafrost zone in mountain environments. However, densely populated settlements and transportation life lines are located at lower altitudes and can directly and/or indirectly be affected by processes occurring in permafrost terrain, requiring in situ engineering solutions such as retention dams (Keller et al., 2002) and the establishment of hazard maps for improved land-use management (Götz and Raetzo, 2002). Much of the infrastructure located directly on/in mountain permafrost pertains either to tourism, communication or power related industries and is of high economic and social significance, in particular in European mountains.

In areas other than the European Alps, hazard potentials related to mountain permafrost are mainly affecting lifelines, such as pipelines, power lines, railways or roads, hydro power infrastructure or mining activities at high altitudes (e.g., Kääb et al., 2005; Wei et al., 2006).

When designing infrastructure or assessing natural hazards in mountain permafrost environments, geoscientists, engineers and decision makers often do not have guidelines available for risk assessment and management, and to help to identify potential problems. Projects successfully completed in Alpine environments, including special anchoring techniques (Phillips, 2006; Rieder et al., 1980; Stoffel, 1995), cooling systems, building materials and innovative geometrical correction systems (Phillips et al., 2007) and site tailored solutions for Arctic infrastructure (Hayley and Horne, 2008) may help with ideas for new designs. Efficient, site- and project-specific monitoring, detailed observations and thorough site investigations developed in parallel have demonstrated the strengths of such joint engineering solutions (Keusen and Amiguet, 1987; Phillips et al., 2007; Steiner et al., 1996).

In this chapter, typical geotechnical hazards and challenges related to mountain permafrost, major geotechnical and geothermal characteristics are presented, as well as suitable field and laboratory investigations. Monitoring programmes are presented and advantages of the observational method are illustrated when building in such environments. Schematics and flow charts are introduced to provide a pathway through the design process. Finally, some examples of successful structures and adaptation methods are presented. By using the tools presented herein, the reader should be able to identify and manage problems, to assess special situations, and to introduce appropriate mitigation and adaptation strategies in a timely manner.

Was this article helpful?

0 0

Post a comment