PHYSICAL MODELING OF RAINFALL-INDUCED LANDSLIDE

Abstract

Rainfall induced landslides are one of the most common and damaging natural hazards in Himalayan region that not only degrade land in hilly areas but additionally causing deaths and destruction on natural slopes (e.g. Hilly areas) and cause tremendous losses. These slope failures usually influence by rain intensities which vary with time that is extremely common in Himachal Pradesh. The intensity and time duration of rainfall over a catchment area decide the property and magnitude of the landslide occurred by the rainfall. Deep slope failure mostly occurred by long duration rain over a catchment area, whereas shallow failure is related to very short-term rain with high intensity. Mostly in shallow slope failure small quantity of soil or debris slides very rapidly. Slope failure which is caused by the rainfall as rain water percolates through the soil layer which in-turn reduces the shear strength of the soil layer.

In Himachal Pradesh a region named Jhakri near NH-5 has recurring slope failure which is broadly affected by the action of rainfall causing significant injury and traffic disruption nearly every year. As NH-5 is only connecting road from outer cities to local areas, stability of slopes on this route have major concern for safe transportation. So this site is selected as a case study for this thesis to study the failure mechanism by the action of rain water, by adopting a physical model. To determine the inherent index properties of soil geotechnical tests has been done in laboratory which affects the stability of existing slope. Further, relation between cumulative rainfall and slope failure pattern has been described.

A physical model is prepared by the theory of semi-similarity which includes the similarity of model size and material used in test and test is performed to examine the failure mechanism occurred by the rainfall with threshold value of rainfall intensity vi

which is based on the landslide failure occurred at the study area. Numerical Modelling has also been done to analyze the stability of slope using GEO5 software. A rainfall generator is also designed and introduce in test to generate the rainfall of particular depth of rainfall.

The study shows that slope geometry and rainfall intensity are the major affecting parameter which generally introduce the landslide by the action of weathering and percolation of water through the soil pores which leads to the development of lubrication effects between soil particles and hence reduction in shear strength parameter of soil. It also indicates that permeability and density of the soil also playing an important role in slope failure mechanism. Relation between cumulative rainfall and slope failure pattern has also been described.