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ENCAMPADANA SLOPE (Principality of Andorra, Pyrenées)
1. Description of the site
 The slope of Encampadana is located close to the village
of Canillo, on the left margin of the Valira d’Orient River, in
the Principality of Andorra.
It consists of phyllites, dark slates and argillaceous limestone of
Devonian age, and black carbonaceous shale of Silurian age. The slope
has developed a mechanism of sagging. The morphological features that
characterise the movement are a large graben close to the ridge and
up-slope and up-movement facing counter-scarps. Many sagging phenomena
are known to be controlled by systems of foliation surfaces or joints
striking approximately parallel to the hillside and dipping at steep
angle (T-sagging) while single-sided sagging (rotational sagging) may
result from deep-seated deformation or mass creep. The site of Encampadana
displays two systems of rock joints and foliation and, on the other
side, in the lower part of the slope there is an exposure of black carbonaceous
shale highly deformable. Therefore, both sagging types are possible
at Encampadana.
1. Description of the site
The slope of Encampadana is located close to the village
of Canillo, on the left margin of the Valira d’Orient River, in
the Principality of Andorra.
It consists of phyllites, dark slates and argillaceous limestone of
Devonian age, and black carbonaceous shale of Silurian age. The slope
has developed a mechanism of sagging. The morphological features that
characterise the movement are a large graben close to the ridge and
up-slope and up-movement facing counter-scarps. Many sagging phenomena
are known to be controlled by systems of foliation surfaces or joints
striking approximately parallel to the hillside and dipping at steep
angle (T-sagging) while single-sided sagging (rotational sagging) may
result from deep-seated deformation or mass creep. The site of Encampadana
displays two systems of rock joints and foliation and, on the other
side, in the lower part of the slope there is an exposure of black carbonaceous
shale highly deformable. Therefore, both sagging types are possible
at Encampadana.
2. Hazard analysis
Until now geological, structural and geomorphologic
reconnaissance of the landslide site have been conducted. Several trenches
have allowed for the identification of several activity periods in past.
Recent surveys (1998) show activity signs in the upper part of the slope.
It is intended to carry out at least four measurement campaigns by differential
GPS at selected points representative of the different parts of the
sagging.
For the numerical modelling of the site, a three-dimensional model of
the site (including the main geological, geomechanical, topographic,
etc., features of the area) will be defined. The model will then be
used to analyse and predict the movements of the slope by means of finite
element analysis with our own software.
3. Elements at risk
The slope affected has an extent of more than 1 km
in length, a height of 800 m and the volume of the mobilised mass involves,
at least, several tens of millions of cubic meters. An important ski
resort is located in part of the Encampadana slope while at the bottom
of the valley there is a small village (El Tarter) and the main road
linking Andorra with the French border. The collapse of the Encampadana
slope would cause the damming of the Valira d’Orient River, threatening
the town of Canillo and other downstream communities.
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