Mass Wasting - Hydrogeology: Objectives, Methods, Applications - page 250

• the departmental road 2205, which passes below the foot of the slide
and leads to Saint-Etienne-de-Tinée, was rerouted in 1985 to the right
bank, in order to follow a less exposed path;
• a diversion gallery for the Tinée was built from 1989 to 1991, in order
to alleviate the potential obstruction of the valley if the slide were to
brutally set itself back into motion.
2.5 Example of the Ardisson landslide (La Trinité, Alpes-
Maritimes)
During the construction work for the Paillon-Turbie section of the A8
highway linking the Nice area to Italy, a sizeable landslide in 1977 affected
an embankment at a location called “Ardisson”.
The highway passes through the subalpine range of Nice, structured as
a series of east-west folds thrusting over each other towards the south. It is
locally set into the northern fl ank of the Mont Camps-de-l'Allée unit, held
up by the Jurassic limestone that outcrops widely on the overlooking ridge
and that is covered on the slope by Cenomanian marl, then by Turonian
marl-limestone. Despite the east-west brittle and ductile deformation
affecting the Cretaceous formations, the series is globally monoclinal and
is cut across by sizeable north-south transverse faults (Figure 123).
The Ardisson embankment is made up of unsorted limestone and a
marly core, over a length of 400 meters and a maximum height going from
10 to 20 meters. It allows the highway to cross a large concave section of
the slope, with a transversal slope of 10 to 15°, the Cenomanian marly
substratum of which is masked by a more or less developed scree cover.
The landslide occurred following a signifi cant rainy episode, in a rapid
evolution, with movements of 1.0 to 1.5 meters per day in certain sections
during active periods, and over a large areal extent, since it affected an area
of 6 hectares and set into movement a volume of material of over a half a
million m 3 . It was visible on the ground as a classic slide, characterized by
is crowning scarp cutting into the embankment, by lateral shear fractures
limiting a stepped body, and by a toe mass locally channeled by a small
ravine (Figure 123).
These disorders are in fact located on an ancient landslide, of greater
magnitude, which was partially remobilized during the highway
construction work. They are worrisome indicators for the future stability
of the highway platform and for the immediate security of the residences
located downslope.