The present papers deals with in situ characterization of rock formations as per Schmidt Rebound Hammer classification values (R) and portrays a model for spatial susceptibility of landslides in mountainous terrain. A geotechnical classification of rock masses depending on the range of R-value has been proposed and a regional correlation with the structural features traversing in the area has been attempted. Rebound values have been utilized to estimate the geo-mechanical properties of in situ rock to categorize the different lithological assemblages into geotechnical units of varying competencies. Geotechnical units assigned weightings of slope parameters, structure and bedding relations, land use and land cover etc and the terrain has been categorized into susceptibility classes such as very low, low, moderate, high and very high depending on the spatial probability of landslide occurrence highlighting relative severity of landslide hazard.
Rock mass characterization offer many geotechnical challenges as the rock behaves in many different ways in its natural geological environment owing to inherent lithological and structural variations. At times these inherent characters are alone not sufficient to understand the behavior of rock mass under loading and excavations for major civil engineering structures. In an attempt to provide guidance on the properties of rock masses a number of rock mass classification systems have been developed. The most widely known classifications are the RMR system of Bieniawski (1973, 1989) and the Q system of Barton, Lien and Lunde (1974) etc. The classifications include information on the strength of the rock material, the spacing, number and surface properties of the structural discontinuities as well as allowances for the influence of subsurface water, in situ stresses and the orientation and inclination of dominant discontinuities. The strength parameters used are invariably the laboratory tests done on the rock samples which may not represent in situ strength of the rock mass. The present paper deals with characterization of rock formations according to the Schmidt rebound hammer classification values (R) which have been used in rock mass characterization.
Rebound values have been utilized to estimate the geo-mechanical properties of in-situ rock to categorize the different lithological assemblages into Geotechnical Units of varying competencies. A case of such geotechnical classification has been attempted in parts of Kali River valleys of Eastern Kumaun Himalaya in order to portray a model of spatial susceptibility of landslides. The likelihood of landslides in such hilly terrains exposing the bedrock along their slopes is, largely dependent on the strength of the rock mass besides other factors that are known to govern the occurrences of landslides.