Browsing by Author "Thomas, B.C."

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Erosion Studies on Lithomargic Clays
(2019) Thomas, B.C.; Shivashankar, R.; Jacob, S.; Varghese, M.S.
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.
Erosion Studies on Lithomargic Clays
(Springer, 2020) Thomas, B.C.; Shivashankar, R.; Jacob, S.; Varghese, M.S.
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/m2, whereas for soils with higher clay fraction and fine sand content the critical shear stress varied from 200 to 400 N/m2. 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.
Laterites and lateritic soils: Geology, engineering properties and problems
(International Association of Lowland Technology 1 Honjo Saga 840-8502, 2020) Shivashankar, R.; Thomas, B.C.
Lateritic soils are abundantly available in the Konkan belt in the western coast of peninsular India, in the four southern states namely - Kerala, Karnataka, Goa and Maharashtra. Along with heavy rainfall (annual rainfall of 2000mm - 4000mm), the region is characterised by high humidity and little variation in temperatures. The typical stratification in lateritic areas consists of soft to hard lateritic crust at the top - about 3m thick, underlain by a layer of lithomargic clay (8 to 10m thick) underlain by parent rock, which is granitic gneiss. This paper briefly discusses the following aspects of lateritic soils (a) geotechnical properties, including those of laterites, lithomargic clays, lateritic lithomarges and lithomargic laterites (b) erosion studies from hole erosion tests (c) slope stability problems of excavated slopes in lateritic formations (d) role of vegetation i.e. turfing and/or trees on slopes in the stability of slopes. It is concluded that lateritic soils, especially lithomargic clays and lateritic lithomarges (1) behave somewhat like dispersive soils. (2) They are highly erosive by nature, especially lithomargic clays with higher content of sand and silt (3) Stability of both excavated and embankment slopes depends on good drainage control. Providing berms and vegetation on slopes adds to stability of slopes. © 2020 International Association of Lowland Technology. All rights reserved.
Slope stability studies of excavated slopes in lateritic formations
(Springer, 2019) Shivashankar, R.; Thomas, B.C.; Krishnanunni, K.T.; Venkat Reddy, D.V.
The study area for this paper is coastal Karnataka in India, which has laterites and lateritic soils. The soil stratification in this area mainly consists of lithomargic clay, which is a product of laterization, sandwiched between the hard and porous weathered laterite crust at the top and the hard granite or granitic gneiss underneath. This lithomargic clay, locally called as ‘shedi soil’ behaves as dispersive soil and is also highly erosive. In the first stage of this study, laboratory erosion studies are conducted by using the hole erosion test apparatus on controlled shedi soil samples. Erosion observed in the HET is accelerated due to slaking irrespective of dispersive nature of the soil. Erosion problems were also dealt with using a stabilizer, calcium lignosulfonate and resulted in high increase in its erosion resistance. In the second stage of this study, slope stability studies of excavated slopes in lateritic formations are conducted considering intensity of rainfall, ponding and seepage, apart from the usual geotechnical parameters. The slopes steeper than 60° are not stable in the case of shedi soil considered here. © Springer Nature Singapore Pte Ltd 2019.