Landfills of hazardous waste like radioactive rest products with low activity, orashes from incinerated organic waste, need to have top clay liners for minimizingpenetration and percolation of precipitated rain and meltwater. Temperature anddry weather vary interchangeably with wet periods making the clay desiccate andfissure, and subsequently wetted etc. Top liners are commonly made of smectiteclay, which is the best isolating soil material, undergoing swelling and shrinkageto an extent that depends on the clay content and density. The most importantquestion is whether such liners, in unfrozen condition and covered by erosionresistingcoarse soil, maintain their coherence and tightness after centuries ofhydration/dehydration cycles. The present study, made on physically confined softIraqi clay with about 30% smectite indicates that initially homogeneous dense clayshrinks and desiccates and becomes fissured at 30oC and room RH, but partlyrecovers by becoming water saturated by infiltrated water. A limited number ofdrying and wetting sequences seem to give approximately the same change,suggesting that, under common weather conditions and lack of externaldisturbance, such liners retain a considerable part of their initial water tightness.Thick liners with moderately to high density and exposed to loading by overlyingcoarse fill are expected to serve particularly well.
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