Anisotropic swelling in black cotton soil

The influence of initial moisture content and the nature of granular material on the anisotropic swell behaviour in black cotton soil has been examined. It was observed that the amount and rate of swelling are guided by the initial particle orientation. For samples compacted with moisture below the optimum value, the variation in swelling trends in vertical and horizontal directions is a result of the particle arrangement, the pressure exerted by the air in the voids and also the subsequent expulsion of the same. In samples compacted with moisture content above the optimum, the initial dispersed state of the particles guides the anisotropy. The swelling in such samples is considerable in directions transverse to the particle orientation. At optimum moisture levels, because of the minimal differences in the particle arrangement for samples in vertical and horizontal directions, the swelling is similar in both cases and as such no anisotropic behaviour was noticed. Increasing presence of granular component in the soil reduces the rate of swelling, protracts the time for completion of swelling and also reduces the anisotropic behaviour. Reduction in the grain size of the granular material facilitates quick swelling. The variations in such samples for vertical and horizontal directions are explained on the basis of packing in the system and the constraints imposed by sand grains on osmotic swelling. Since similar variables exist in field conditions, the present study enables an understanding of their role in the anisotropic swell behaviour of black cotton soils.