Study of Nilgiri Hills A Landslide Prone Area and its Seepage Analysis

Abstract

India is among the top ten countries with the highest percentage of landslide fatalities for the past few years. Intense rainfall during the monsoon in 2009 in the hilly district of Nilgiris, in the state of Tamilnadu in India, triggered landslides at more than three hundred locations which affected road and rail traffic and destroyed number of buildings that left more than forty people dead and hundreds homeless. In this report three case histories are investigated: failure of slope in a railway track at Aravankadu , failure of retaining walls supporting buildings at Coonoor, failure of slope and retaining wall along national highway at Chinnabikatty. Laboratory investigations are carried out on soil samples collected at the sites. Soils at all the three locations have high fine content and low values of coefficient of permeability. Finite element analyses of all the three case histories were carried out using PLAXFLOW software to understand the failure mechanism and contributing factors to determine the critical slip surface and factor of safety. Safety analysis using flow field technique is carried out for the slope at Aravankadu..Degree of saturation and pore pressure of Coonoor site revealed that the zone of intense shearing behind the retaining walls due to combined effect of surcharge loading of building and generated pore pressure.