Geotechnical problems caused by glaciolacustrine clays in the French Alps: Fid-Bau Portal

Geotechnical problems caused by glaciolacustrine clays in the French Alps

Giraud, A. / Antoine, P. / Van Asch, T.W.J. / Nieuwenhuis, J.D.

Abstract After more than 10 years of observations and monitoring of several landslides in glaciolacustrine clays in the French Alps, the authors give an account of the physical and mechanical characteristics of these formations. The physical and geomechanical properties of the clays are analysed in relation to the main types of instability observed on the natural slopes of the area studied. The low plasticity indexes of these clays explain the rapid transformation of the clays into a liquid state leading to innummerable surface flows. The clays show a strong anisotropy at peak strength conditions that disappears at residual strength (c′= o; ø′=16–18°). Natural slopes become unstable if the gradient exceeds 8 – 10. These types of movement can be distinguished at three different depths (0–5 m; 5–10 m and greater than 10 m). The displacement rates vary from 1 cm/yr for the deep-seated slides to as much as 1 m/yr for the surficial slides. Displacement rates in these slides are limited by the viscous properties of the laminated clays. However, extreme rainfall may cause catastrophic failure. In conclusion, some recommendations are given from an engineering point of view.