Sensitivity of rock slope stability in relation to thermal regime – examples from Norway

Abstract:

The steep topography in western and northern parts of Norway includes large unstable rock faces terminating into narrow fjords and lakes. The large number of such unstable faces lists rock slope failures as one of the bigger hazard threats in Norway.

Successive studies have revealed presence of permafrost in Norway and a number of the unstable rock slope faces are located in mountain permafrost regions. It is known that thawing permafrost influences the rock-mechanical interplay in the bedrock and can hence play a role in the early stage of destabilization in rock walls. At present, both borehole measurements and several modelling studies for Norwegian mountains clearly indicate increasing ground temperatures during the last decades. As a first step in this study, a numerical study of the sensitivity of permafrost to climatic changes was performed for a number of sites along a latitudinal transect in Norway.

Together with the thermal condition, lithology, structure and inclination are important conditions for the force regime in rock walls. In this study, the nature of temperature dependence on rock wall stability has been investigated through numerical modelling and the sensitivity of different factors related to these conditions has been evaluated in terms of stability, including the thermal regime. The focus has been on the initial conditions that are important for typical Norwegian rock wall sites and in particular for the sites where the simulations of the permafrost sensitivity have been performed. The analysis was applied for the Nordnes mountain in northern Norway, which is continuously surveyed due to the possible danger if large rock falls may hit the fjord water body generating tsunamis.