Faculty Publications

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Performance of granular columns in dispersive soils
(Thomas Telford Services Ltd ttjournals@ice.org.uk, 2014) Nayak, S.; Dheerendra Babu, M.R.; Shivashankar, R.; James, N.
The soils found abundantly along the Konkan belt in peninsular India are lateritic soils and lithomargic clays. The locally available lithomargic clayey soils are problematic in the sense that their strength reduces drastically under saturation conditions, which is typical behaviour of the dispersive type of soil. Most foundations are placed on this soil layer. This paper presents results from a series of laboratory plate load tests carried out in unit cell tanks to investigate the behavior of granular columns in these weak (lithomargic clay) grounds. Tests are carried out with two types of loading: with the entire area in the unit cell tank loaded, to estimate the stiffness of the improved ground; and with only the granular column area loaded, to estimate its limiting axial capacity. Investigations were carried out by varying the area ratio (or spacing), diameter of granular columns, end condition and column configuration. The load-settlement behaviour, stiffness and bulging behaviour of granular columns are analyzed. It is found that the ground treated with granular columns exhibits a high load-carrying capacity and stiffness, and a significant reduction in settlement, compared with the untreated ground. © Ice publishing: All rights reserved.
Some studies on engineering properties, problems, stabilization and ground improvement of lithomargic clays
(Southeast Asian Geotechnical Society seags@ait.ac.th, 2015) Shivashankar, R.; Ravi Shankar, A.U.; Jayamohan, J.
The study area for this paper is coastal Karnataka in India. The area has laterites and lateritic soils, and also a large number of sporadic lateritic hillocks. The soil stratification mainly consists of lithomargic clay sandwiched between the weathered laterite at top and the hard granitic gneiss underneath. Quite often the top laterites are removed in this area for use as bricks for construction purposes, thus exposing the underlying lithomargic clay. This coastal area receives copious amount of rainfall and a lot of developmental activities are taking place. These lithomargic clays, locally called as 'shedi soils' are also used as fill material in low lying areas, very often adjacent to water bodies. These soils behave as dispersive soils and are also highly erosive. A lot of engineering problems - such as foundation problems, subgrade problems, erosion and slope stability problems are being faced due to the presence of these shedi soils. Some laboratory studies on the engineering and strength properties of these lithomargic clays and stabilized soils, Ground Improvement on shedi grounds are made and reported.
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.

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