Geotechnical investigation and slope stability analysis of Kallarkutty earth slide, Idukki District, Kerala, South India

ABSTRACT The earth slides that occurred in the Kallarkutty area, Idukki District, Kerala, South India in 2013 and 2017 were studied to identify the causative factors and to suggest the mitigative measures. Geological, geophysical and soil mechanical properties of the area have been studied and the uni-dimensional infinite slope stability model (Mohr-Coulomb failure law) was attempted to calculate the Factor of Safety (FoS). FoS values in three different pore pressure conditions, i.e., as dry, 50% and 100% saturation indicate that stability decreases with saturation. In the downslope side of area towards the cliff edge, the FoS value is less and hence unstable. The landslides in the study area are translational with slip plane being the interface of rock and overburden. The geological factors augmenting the slide is loosely consolidated overburden over the foliated gneiss. The removal of toe support and unscientific slope modification without support intervention by excavation through overburden material rich in lithomarge are the main preparatory factor whereas the pore pressure increment aided by heavy rainfall is the triggering factor. Based on the study, corrective measures, and precautions to avoid further slides have been suggested.