Dispersive behavior of nonswelling clays

Abstract

This paper examines the possible factors that contribute to the dispersive behavior of compacted nonswelling clays and proposes the use of a synthetic organic stabilizing agent to reduce the dispersive tendency of such soils. Results of chemical tests on saturation extracts of the clays tested failed to identify them as piping susceptible. However, pinhole tests on statically compacted specimens showed the materials to be intermediate (ND3, slightly to moderately dispersive clays that slowly erode under 180 or 380 mm head) to completely dispersive (D1 dispersive clays that fail rapidly under 50-mm head). Use of a concentrated salt solution (2N CaCl₂) and a solvent with lower dielectric constant (methanol, dielectric constant = 32.6) did not reduce the dispersive tendency of the compacted kaolinite in the pinhole test (diameter of hole = 1 mm), suggesting that deflocculation triggered by diffuse double layer repulsion does not contribute significantly to the dispersive tendency of nonswelling clays. Pinhole tests conducted with variously saturated (33 to 84%), compacted kaolinite specimens (γd = 1.28 Mg/m³ in all instances) suggested that compression of entrapped air in the voids by capillary absorption of water is not the primary factor causing dispersion of nonswelling clays. Experimental results showed that pinhole test classification of statically compacted kaolinite changes from D1 (dispersive) to ND3 (intermediate) on reducing the remolding water content from wet of optimum (w = 34%) to a dry of optimum (w = 27%) value. The differences in structure of the compacted clay due to differences in molding water content are considered responsible for the higher erosion resistance of the compacted kaolinite on lowering the molding water content. Subsequent lowering of water content below 27% has no further influence on the pinhole test classification of the compacted clay. The use of a synthetic long chain organic polymer, poly vinyl alcohol (PVA), in improving the resistance of compacted nonswelling soils was tested. The addition of 1% PVA solution to kaolinite transforms the nonswelling clay from dispersive D1 to the dispersive D1/D2 category suggesting that the long chain organic polymer can improve the dispersion tendency of nonswelling clays to a slight extent.