Clay minerals in black cotton soil expands and seeks more space as the soil mass get saturated with moisture. This process generates pressure exerted in all directions. The direction and magnitude of soil movement will depend upon the magnitude of the confining pressure at any particular point of resistance. Soil movement will be minimized where confining pressures are the largest while movement will be greatest where the magnitude of the confining pressure is the smallest. Molecular structure of black cotton soil is explained in previous post.
