Erosion rates of unsaturated compacted calcium montmorillonite and sodium montmorillonite clays were measured under a range of tractive shear stresses in a rectangular flume. the calcium montmorillonite was treated with calcium chloride and sodium carbonate to obtainsamples with different chemical composition. Samples were compactedat nearly optimum water content under 700 pa into sample containerswith 160-sq cm surface area and subjected to flowing water in the flume. The tractive stress on the bottom of the flume was determined by measuring the velocity distribution of the flow and using the prandtl-von karman equation. The tractive stress ranged from 1.67 to 12.9 pa. The erosion rate of naturally occurring calcium montmorillonite was two orders of magnitude higher than that of sodium montmorillonite. When calcium montmorillonite was treated with 0.88 percent bydry weight sodium carbonate, the erosion rate was reduced to the same order as that of sodium montmorillonite. Addition of calcium chloride had no appreciable influence on the erosion rate of calcium montmorillonite. Empirical equations have been developed to estimate the erosion rate of compacted unsaturated montmorillonite clay as a function of sodium adsorption ratio and tractive stress. This paper appeared in transportation research record no. 1151, hydraulic erosion. For covering abstract see irrd no 818454.
Abstract