Erosion Rate of Dispersive and Nondispersive Clays

Abstract

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. Samples are compacted at near the optimum water content and subjected to flowing water in the flume. The tractive stress is determined by measuring the velocity distribution of the flow and using the Prandtl-von Karman equation. 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.