Guillaume Favre-Bulle: Instabilités rocheuses le long de la route nationale 7 Secteur Guido – Uspallata (km 1118 à 1133) Provincia de Mendoza – Argentina.

Guillaume Favre-Bulle
Co-supervisors: Prof. Michel Jaboyedoff, Valérie Baumann, Andrea Pedrazzini

The National Road 7, important link between Argentina and Chile, is subject to many natural hazards, threatening the vehicles travelling along. This work aims to classify the risk associated with falling blocks, to intervene as a priority on the most dangerous places to avoid investing in useless protective measures.

The study area is located west of the city of Mendoza in the Andes. The road passes several times along rocky outcrops that may be highly fractured and let blocks free. The analysis was conducted on two points: a GIS analysis of the DEM (Digital Elevation Model) and a field study. The GIS analysis has called for the creation and the search for a DEM of good quality. After several trials with satellite images and the SRTM, pairs of stereoscopic aerial photographs of 1966 have given the least bad outcome. These DEM are strongly deformed in places and do not reproduce accurately the topography.

The GIS analysis is based entirely on the study of the geometry of the DEM, the result is related to quality. Several factors are summed together : rock instabilities for the break susceptibility, slope, slope orientation, kinematic tests of the main discontinuities and SLBL. The results are used for propagations simulations of falling blocks. The results are not very good because of the poor quality of the DEM. Areas with high failure susceptibility are numerous and extensive, making it impossible to establish priority areas. The Conefall propagation can not be calibrated with field data and the results are indicative only.

On the field, discontinuities outcrops were measured and used to calculate several classification methods: RMR, SMR, and GSI. The results give rock masses of good quality, but can be very unstable following the geometry of the discontinuity and the slope of the outcrop. Then, two RHRS methods were calculated on each outcrop to classify them in order of priority for intervention. Both methods (RHRS Budetta and RHRS Colorado) take into account the characteristics of the slope, climate, geology and exposure of vehicles to danger. Both methods were compared and it is the Colorado RHRS which was recommended for future studies.

The RHRS allowed to classify outcrops for priority of intervention. Sites with the highest scores will be subject to further study to determine what protective measures will be most suitable and the money will be managed in the best possible way.