EROSION RATE OF DISPERSIVE AND NONDISPERSIVE CLAYS.

Erosion rates of unsaturated compacted sodium and calcium montmorillonite clays are measured under a range of tractive shear stresses. The calcium montmorillonite is treated with additives calcium chloride and sodium carbonate to obtain samples with different chemical compositions. The tractive stress ranges from 1. 67-12. 9 Pa. The erosion rate of calcium montmorillonite (a nondispersive clay) is two orders of magnitude higher than that of sodium montmorillonite (a dispersive clay). When calcium montmorillonite is treated with 0. 88% by dry weight sodium carbonate, the erosion rate is reduced to the same order as sodium montmorillonite. Empirical equations are developed to estimate the erosion rate of compacted unsaturated montmorillonite clay as a function of the sodium adsorption ratio and tractive stress.