Shrinkage and desiccation cracking in bentonite-sand landfill liners

Data are reported on the shrinkage and desiccation cracking exhibited by be ntonite-enhanced sand mixtures (BES) upon air-drying. Mixtures containing 1 0 and 20% bentonite by dry weight, compacted at moisture contents ranging f rom 8 to 32%, were investigated. Hydraulic conductivity data for BES specim ens saturated and tested immediately after compaction, and for similar spec imens that had no visible damage after air-drying, are also presented. All the mixtures exhibited volumetric shrinkage upon air-drying with the am ount of shrinkage increasing with increasing moisture content during compac tion. Ar any initial moisture content mixtures containing 20% bentonite shr ink more than those containing 10% bentonite, but the shrinkage is insensit ive to the compactive effort. Compacted beds of BES containing 10 and 20% b entonite exhibit no visible desiccation cracking as the top surface is drie d when compacted at 15 and 14% moisture content, respectively, and only min or cracking when compacted at initial moisture contents of 20 and 15%, resp ectively. For the range of mixtures tested, it appears that cracking only o ccurs when BES undergoes more than about 4% volumetric shrinkage when air-d ried. The saturated hydraulic conductivity of intact BES specimens is unaff ected by a drying episode prior to testing. (C) 2001 Elsevier Science B.V. All rights reserved.