The clay mineral-based soils having low permeability and high swell–shrinkage characteristics are preferred as a backfill and buffer material for containing hazardous waste. Though many factors influence the behaviour of these soils, the contribution of various particle sizes present in them is not thoroughly investigated. In order to examine the effect of particle size on electrokinetic, mineralogical and surface properties of soils, the selected soils were sieved through different size of sieves such as 75, 63, 54, 45, 36, 25 and 20 µm, and the fractions retained on them were collected. The collected fractions were processed and characterized for their electrokinetic, mineralogical and surface properties. Based on the experimental results, the role of different particle size on the micro- and macro-level behaviour of selected soils was quantified. © 2020, Springer Nature Singapore Pte Ltd.