Deep-seated failure propagation in a fractured rock slope over 10,000 years: The La Clapière slope, the south-eastern French Alps |
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| Authors: | Samyr El Bedoui Yves Guglielmi Thomas Lebourg Jean-Louis Prez |
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| Institution: | aUMR Géosciences Azur-CNRS-UNS-IRD-UPMC, 250 Avenue Albert Einstein, 06560 Sophia-Antipolis, France;bCentre d'Etudes Techniques de l'Equipement Méditerranée-Laboratoire régional de Nice, 56 Bd Stalingrad, 06359 Nice Cedex 4, France |
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| Abstract: | The “La Clapière” area (Tinée valley, Alpes Maritimes, France) is a typical large, complex, unstable rock slope affected by Deep Seated Gravitational Slope Deformations (DGSD) with tension cracks, scarps, and a 60 × 106 m3 rock slide at the slope foot that is currently active. The slope surface displacements since 10 ka were estimated from 10Be ages of slope gravitational features and from morpho-structural analyses. It appears that tensile cracks with a strike perpendicular to the main orientation of the slope were first triggered by the gravitational reactivation of pre-existing tectonic faults in the slope. A progressive shearing of the cracks then occurred until the failure of a large rock mass at the foot of the slope. By comparing apertures, variations and changes in direction between cracks of different ages, three phases of slope surface displacement were identified: 1) an initial slow slope deformation, spreading from the foot to the top, characterized by an average displacement rate of 4 mm yr− 1, from 10–5.6 ka BP; 2) an increase in the average displacement rate from 13 to 30 mm yr− 1 from the foot to the middle of the slope, until 3.6 ka BP; and 3) development of a large failure at the foot of the slope with fast displacement rates exceeding 80 mm yr− 1 for the last 50 years. The main finding of this study is that such a large fractured slope destabilization had a very slow displacement rate for thousands of years but was followed by a recent acceleration. The results obtained agree with several previous studies, indicating that in-situ monitoring of creep of a fractured rock slope may be useful for predicting the time and place of a rapid failure. |
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| Keywords: | Progressive failure Surface displacements La Clapiè re DGSD |
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