In the Western Ghats during rainy season, landslides cause extensive damage to life and property and also blocks many communication routes. Geological Survey of India being Nodal agency for landslide studies in India, has taken up the geotechnical studies of these landslides, in order to understand landslide causes, mechanism, suggest remedial measures and ultimately to develop an early warning system. The landslide at Hilary village was chosen as a model to conduct site specific studies, which includes geotechnical mapping, preparation of L- sections and collection of a few undisturbed and disturbed soil samples for analysis. The hill slopes are essentially covered with highly porous lat erotic soil which permits ample water infiltration at much deeper levels making the slope highly unstable on super-saturation during heavy downpour. Rise in flow level of stream lets facilitates gradual erosion of toe support which ultimately facilitates downward movement of super-saturated overburden situated on the inclined slope. Modification of slopes for practicing agriculture, slope loading by construction and alteration of natural drainage has contributed to the frequent landslide incidences in the Western Ghats.
Hilary (17°54'55" N: 73°45'45" E, too. no. 47 G/13) is a small village located in Tensile Mahabaleshwar, District Sahara, Maharashtra. The average annual rainfall ranges between 2500 to 3500 mm out of which, June, July and August accounts for most of the precipitation. Vegetation is thick to moderate containing tropical flora. The area exhibits highly rugged & closely dissected hilly terrain. Main topographic features are flat plateau tops, moderately sloping to vertical scarps, „V" shaped valleys and step like terraces characterized by sudden break in slope formed due to Deccan Basalt lava flow contacts. General pattern of land use is, location of small villages, hamlets and residential dwellings at the higher contours occupied by flat Deccan Trap plateau tops. Lower elevations and the hill slopes are occupied by agricultural lands. Agriculture is the main occupation and terrace cultivation along the hill slopes is the most common type of agricultural practice. Geological setup of the study area The area exposes about 250 m thick pile of Deccan Trap lava flows of Mahabaleshwar Formation of Sahyadri Group. The lava flows are essentially a'a type and moderately to highly porphyritic. These lava flows are divided into three groups. The Landslide area is mainly occupied by Flow Group III (Flows 21 to 29). These lava flows are jointed with prominent sets trend NISSE, N-S, NE-SW having vertical to sub-vertical dips.
Site specific geotechnical investigation includes study of general topography, lithology and geological setup, different lido units in the affected area, their probable thickness, study of the failing slope & qualitative strength of slope forming materials, anthropogenic activities, ground deformations, nature of movement and possible reasons for the failure.
It comprises 4 types of lido units.
lat erotic soil/clay (lit homage)
highly weathered basalt &
fresh basalt. Late rite occurs as patches at different levels.