Water permeability, water retention and microstructure of unsaturated compacted Boom clay

摘要

Three classes of experiments are considered in thispaper to provide information for two artificially prepared Boomclay fabrics: mercury intrusion/extrusion tests; mainwetting/drying paths; and water inflow/outflow transient(permeability) tests. These tests, which are ususlly treatedseparately, are joined in a common reference frame to provideinformation about the morphology of the porous medium andfactors influencing Boom clay unsaturated hydraulic states withreference to water retention curves and relative waterpermeability values. The main objective is to interpret mercuryintrusion porosimetry results in order to define an entrance poresize region at ca 130 to 180nm separating inter-aggregate andinter-aggregate zones. This pore size region is further associatedto a delimiting zone in the retention curve separating regions of'intra-aggregate governing suction' at gravimetric water contentslower than 13-15% (gravimetric water content is not affected bymechanical effects) and 'inter-aggregate governing suction'9gravimetric water content is sensible to mechanical actions).This water content is further used to define a threshold zonearound a relative water permeability of kW/ kW =0.01 delimiting azone of greater water relative permeability from others thatpresent a restricted flow in a generalised Darcian sense. All theseresults are consistent with the existence of two main pore sizeregions: an intra-aggregate porosity with quasi-immobile waterthat is little affected by loading processes and an inter-aggregateporosity for which the loading mechanism results in a reductionof interconnected macropores affecting free water. Testing resultsshow that intra-aggregate water represents between 54 and 59%of the total volume of water in soil in a low-porosity packingcompacted at a dry unit weight of 13.7kNm-3.