Comparative Study of Index Properties of Natural Expansive Soils with Bentonite-Sand Mixtures

Abstract

 Expansive soils are characterized by its high variation of volume due to the modification of their conditions of equilibrium. This unusual characteristic of the expansive clayey soil makes it difficult to construct foundation in such soil. To overcome  shear failure, development of cracks of the structure, Geotechnical engineers need to select the type of soil which is best suitable and provides a hard soil strata to the foundation. Index properties are known to be indicative of the engineering properties. Simple test required for index properties are known as classification test. 20% of India's land area has been covered by expansive soil for about 0.8 million square kilometre. The majorly covered areas are namely states of Maharashtra, Gujarat, southern parts of Uttar Pradesh, eastern parts of Madhya Pradesh, parts of Andhra Pradesh and Karnataka. The expansive nature of the soil is mainly due to the presence of a clay mineral called Montmorillonite in addition to Kaolinite and Illite which forms the major group of clay minerals. The percentage of clay fraction present in the soil contribute significantly in governing the index properties of swelling soils. In the present study, three natural soil samples indicative of shrink-swell potential consisting varying percentages of fines and respective percentages of sand were considered and an attempt has been made to compare their index properties with that of commercially available Bentonite and sand mixtures with the same design mix proportions. A detailed experimental investigation was done to assess the physical properties and finally the empirical correlations have been built among the various natural soils and also to that of Bentonite and sand mixtures.