Fig.
2 : View of the present state of the cliff after the rockfall.
The road is reconstructed.
Fig.
3 : Picture of the rockfall of Fey deposit.
On
9th January a small rockfall of 2'000 m3 destroyed
the road joining Sion to Fey, on the left side of the Rhone valley
(Figs. 1 to 3).
It has
been demonstrated that this small rockfall is linked to unfavorable
parameters, i.e. occurrence of:
- A
fault
- The
excavation produced by the construction of the road
- An
ancient active cliff
- Unfavorable
rock discontinuities
- Etc.
Furthermore,
the important integrated antecedent precipitation indicates that the
rain can be assumed as a triggering factor. Fatigue and weathering
increased by percolating water must be also considered as a degrading
factor of the rock mass (Fig. 2 and 4).
Fig. 4: Schematic structure and mechanism of the Fey rockfall.
Fatigue led to bulging of the the toe of the wedge J4-J5 (from Baillifard
et al., 2003).
References:
Baillifard,
F., Jaboyedoff, M. & Sartori, M.,(2003): Rockfall hazard mapping
along a mountainous road in Switzerland using an empirical approach.
Natural Hazards and Earth System Sciences.3, 435-442. (Abstract)
Picture
from Crealp
