Detection of Permafrost and Foundation Related Problems in High Mountain ski Resorts

Abstract

The ground ice contained in screes with various rock debris (“rock glacier”) is the most common form of permafrost currently encountered in the Alps between 2500 and 3200 m asl. This altitudinal range is exactly the one which is concerned with the development of major ski resorts. In the manner of glaciers, rock glaciers will move on the slopes as a result of creep of the ice. However, because of the presence of rocky debris, the internal friction slows the movement. Confirming the presence of ice in the ground can be based at first on ground temperature measurements. But regarding the distribution with depth, in the absence of soundings technically and economically difficult to achieve, the geophysical methods provide good results. In the current context of climatic change, the problem of foundations of structures is increasingly taken into account. The observed warming in the Alps causes a slow melting of permafrost; settlements and collapses are observed. Geotechnical studies to illustrate this behavior are of the two following types: (i) feasibility study upstream projects, in order to define areas of permafrost and to avoid them for optimizing the implementation of the works; (ii) diagnostic studies giving solutions for reinforcement works after disorders due to the evolution of permafrost. Two specific examples are given: (i) the choice to draw a line for a chairlift, and (ii) the reinforcement of a ski-lift station with differential settlements.