The rheological beha®ior of a bed of packing material during its consolidation was in®estigated using an elastic-plastic model, the Frictional Material Model. This model takes into account the beha®ior of the packing material under compression stress, its consolidation, its internal friction, its friction against the column wall, and the depen-

The efficiency of chromatographic columns is ad®ersely affected by large-scale radial ®ariations of the packing density or ®oid ratio of the material used to prepare the bed. This heterogeneity is due to wall friction effects that take place during the preparation of the column and to seepage effects operating during the packing process and the subsequent operation of the column. The dependence of the bed's ®oid fraction on the stress applied during its consolidation was determined, as well as its permeability at ®arious stages of the consolidation process and the coefficient of friction between typical packing materials and the stainless steel wall of chromatographic columns. These results are required to de®elop and use numerical models of the ®olumetric response to axial compression of the bed and models of the coupled mechanical-seepage rheology of particulate materials.