Erosion Studies on Lithomargic Clays

Abstract

Lithomargic clays are found at shallow depths in lateritic formations, sandwiched between hard lateritic crust at top and the parent granitic gneiss underneath. Many earlier studies have proved that the behaviour of these soils is similar to dispersive soils, and they are also found to be highly erosive. Very few and detailed studies on erosion of lithomargic clays are available in the literature. Lithomargic clays along the western coastal belt of peninsular India are available with varying percentages of sands and fines (especially silts, with negligible amount of clays occasionally). In this study, a number of hole erosion tests are conducted on controlled lithomargic clay samples with varying percentage of fines to study their erosion characteristics. The influence of degree of compaction, moulding water content, head causing flow, percentage silt content and plasticity index on the erosion rate index and critical shear stress of controlled lithomargic clay samples are being studied. The results of this study indicate that the critical shear stress for soils with higher silt fraction and fine sand content varied from 45 to 125 N/m 2 , whereas for soils with higher clay fraction and fine sand content the critical shear stress varied from 200 to 400 N/m 2 . The erosion rate increased with a decrease in percentage compaction in all the samples, and critical shear stress is found to be highest at optimum moisture content conditions. It is generally observed that soils with fines whose plasticity indices are high, are less erodible compared to soils with fines whose plasticity indices are low. 2019, Indian Geotechnical Society.