Effects of micro- to meso-features on the permeability of fissured clays

This paper discusses the relation of the coefficient of saturated permeability in a given direction, k_i, with the void ratio, e, for fissured and unfissured clays, wherein k_i characterises the hydraulics of the equivalent uniform porous model. The k_i–e data for the fissured clays are compared with what is observed for unfissured clays, either natural or reconstituted. For each clay, the k_i–e data result from laboratory investigation and are related to the fissuring identity of the clay, classified through a fissuring characterisation chart. Through this procedure, the study provides an initial rational insight of the variability of the k_i–e law with both the micro- and the meso-scale clay features. Fissuring is shown to cause meso-scale non-uniformities of the flow patterns, which may cause a variation between the k_i for steady-state seepage and that controlling transient seepage. In general, fissuring increases the clay permeability with respect to the same clay if unfissured and also with respect to the same clay when reconstituted. Also, the study sheds light on the difference between the k_i–e law holding during compression and that during swelling for both unfissured and fissured clays, showing that such difference is more important for fissured clays.