Controlling the destructive effects of clay – organic liquid interactions, by application of effective stresses

Abstract

The magnitude of the effective stresses acting on a clay barrier appear to play a critical role in preserving low hydraulic conductivity, k, during exposure to soluble organic liquids. This paper summarizes the results of a research study on a natural clay from southwestern Ontario permeated with various mixtures of landfill leachate and water-soluble organic liquids at effective stresses ranging from 0 to ~300 kPa. Laboratory testing of "unconfined", water-compacted clays indicated that municipal solid waste leachates containing ethanol and dioxane at concentrations in excess of 70% can cause damaging increases in k of up to 1000-fold. Predamage application of vertical effective stresses can reduce or even eliminate these increases in k because of chemically induced consolidation and closure of macropores that develop as a result of double layer collapse. The levels of static effective stress required to prevent the increases in k were much higher for nonpolar dioxane (> 160 kPa) than for intermediately polar ethanol (20–40 kPa). Postdamage application of static effective stresses successfully eliminated the increases in k produced by ethanol permeation at near zero stress but could not heal the clay damaged by permeation of nonpolar dioxane. The practical significance of this work is discussed relative to clay barrier design. Key words: hydraulic conductivity, clay, organic liquids, leachate, liner, effective stress healing.