Permeability is a key parameter for any containment system including cut-off walls but it tends to be regarded as a fixed property such as strength, sensitive principally to changes in the effective stress or chemical damage. Furthermore chemical attack, if it occurs, tends to be treated as a 'one-off phenomenon. However, a barrier material such as a cement-bentonite is actually chemically reactive system with a dynamic permeability. Flow through this reactor is controlled by the overall permeability of all the reaction zones that develop within it. High permeability reactive barriers (PRBs) are well recognized for the management of contaminated groundwater but low permeability barriers are less often considered as reactors and opportunities for barrier protection and maintenance therefore can be overlooked. This paper is focused on the permeation of water through cement-bentonite materials: much can be learned from this about the dynamic permeability of the reactive matrix that a cement-bentonite material represents.
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