The swelling behaviour of clays

Abstract

In swelling clays two categories of swelling are observed. The first category — the innercrystalline swelling — is caused by the hydration of the exchangeable cations of the dry clay. The second category — the osmotic swelling — results from the large difference in the ion concentrations close to the clay surfaces and in the pore water. The stepwise nature of the innercrystalline swelling can also be seen in the water vapour adsorption isotherm. The swelling stress can be calculated from the isotherm. The measurement of osmotic swelling in the laboratory is discussed. The swelling behaviour of clay rocks depends on the type and quantity of clay minerals encountered, their surface charge and the valence of the cations in the double layer. The swelling properties of the rock can be estimated from its characteristic values. An example for such a calculation is given.