The Swelling of Clay: II. Montmorillonites

Abstract The water content at equilibrium was determined as a function of applied pressure for 35 different Na‐saturated montmorillonites by means of a miniature pressure membrane apparatus. Then the data were used to develop a general, empirical equation in which the swelling pressure of the montmorillonite depends exponentially on the water content. The parameters in this equation were shown to be functions of the cation exchange capacity and specific surface area of the montmorillonite. The data were also used to develop semiempirical equations in which the swelling pressure depends exponentially on the distance between the superimposed layers of the montmorillonite. Depending on the assumptions used in their development, the latter equations involve constant coefficients or coefficients that depend on the surface charge density of the montmorillonite. Analysis of these equations indicated that swelling is due primarily to interaction between the layer surfaces and water.