Preliminary rock-slope-susceptibility assessment using GIS and the SMR classification

The geomechanical classification SMR ( Slope Mass Rating) enables the preliminary assessment of the susceptibility of rock slopes to failure. The SMR index is obtained from Bieniawski's basic RMR ( Rock Mass Rating) through an " adjustment factor" and an " excavation factor". Since its appearance in 1985, this classification has been used for appraisals and preliminary studies in many countries. The method is applied automatically by a Geographic Information System ( Arc- Info GIS). The present study describes the methodology used and the results obtained after mapping the failure susceptibility in rock slopes by computing the SMR index using a GIS. Data have been gathered from the Digital Elevation Model ( DEM), and by the statistical analysis of the parameters measured on the slopes. The methodology has been applied to the slopes along the N- 340 road between Arraijana beach and Castell de Ferro ( Granada, Spain). A total of 40 slopes have been studied along a linear distance of 4 km. As a result, in addition to all the factors that determine the SMR index, the most unfavourable SMR maps as well as the corresponding mean value have been established. From a cross analysis between these two maps and the instability phenomena observed directly in the field, we conclude that the average value of the SMR index calculated for the different discontinuity sets is the most representative value of rock- slope- failure susceptibility. The results show the usefulness of the SMR's parameters to be used in GIS applications to rock- landslide hazard along roads.