Alternative Methods for Wet-Dry Cycling of Geosynthetic Clay Liners

Abstract

Alternative laboratory approaches for cyclic permeation-desiccation experiments on geosynthetic clay liner (GCL) specimens are compared. Permeation cycles for hydraulic conductivity (k) are conducted in flexible-wall permeameters. Subsequent desiccation cycles are conducted using one of three approaches: (1) unconfined desiccation involving drying under controlled relative humidity (RH) with no external stress; (2) axially constrained desiccation involving drying under controlled RH and axial stress simulating one meter of cover soil; and (3) a novel in-permeameter method, where specimens are desiccated without physical disturbance by flushing the permeameter endcaps with controlled-RH gas. Comparison metrics include image analysis of bentonite crack patterns, cycle duration, uniformity of water content, and evolution of k for up to seven wet-dry cycles. All three methods result in similar water content, crack intensity, and hydraulic conductivity response, despite the fact that stress conditions during drying and disturbance to specimens are very different. Observed similarity indicates that internal flaws in the bentonite (e.g., reinforcing fibers), rather than external stress conditions, control desiccation crack initiation and propagation.