Based on the oedometer swell potential values, Holtz and Gibbs (1956) and Seed et al.
(1962) have classified the relative expansivity of the swelling soils. Holtz and Gibbs’(1956)
classification is based on the swell potentials of undisturbed specimens that were inundated
under 1 psi (approximately 7 kPa) pressure. Seed et al. (1962) criterion is based on the swell
potential of remoulded specimens that were compacted at their Standard Proctor MDD
(maximum dry density) and OMC (optimum moisture content) values and inundated under
1 psi pressure. Table 2.1 gives the expansivity categories proposed by these workers.