INFLUENCE OF MATRIC SUCTION ON INSTABILITY OF UNSATURATED SILTY SOIL IN UNCONFINED CONDITIONS

Abstract

Rainfall has been recognized as one of the main causes of natural or manmade slope failure inmany tropical areas of the world. In order to reduce and mitigate rainfall-induced slope failures, there is a needto develop an understanding of reduction in shear strength of soil due to water infiltration. This research aimedat understanding the influence of matric suction on water infiltration and transformation of shear strength inunsaturated soil in unconfined condition. In the present study, two types of test series have been performedusing modern triaxial test apparatus: (1) shear-infiltration test, and (2) pre-wetting shear test. From test results,it was concluded that water infiltration causes the excessive deformations and softening which decreases thecohesion and hence reduces the shear strength of the soil. The more decrease in shear strength was witnessedin case of pre-wetting shear tests and maximum reduction observed was 85% against 36cm3 of infiltrated water.