Measures to Prevent Damages in Black Cotton Soil Areas
Dr. K.M. Soni, Superintending Engineer, CPWD, Bhopal
Black cotton soil, a cohesive soil, is considered a problematic soil for civil engineers. It has characteristics of swelling during rains and shrinking during summer. In both the conditions, it poses problems. During swelling, structure has uplift pressure and produces heave in the foundations, plinth beams, bottom of floors of buildings and canals, roads surfaces etc. and on shrinkage, cracks develop in walls, slabs, plinth protection, floors etc. Though, local construction technology has been developed traditionally in most of the places where such type of soil is found, still cracks are observed in many structures as sufficient precautions are not taken during the construction and maintenance period of the buildings.
Index Properties
Black cotton soil of India has a liquid limit between 60-90%, plastic limit between 30-50% and shrinkage limit about 8-18% as given in Table 1.Black cotton soils having high plasticity index more than 23 described as critical and severe having free swell more than 100% are to be taken special care to avoid cracks in the structures.
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NBM&CW December 2012
