Smear is just what it sounds like, a zone of disturbed soils resulting from the friction of the steel mandrel as it is forced through the soft clays.  In laboratory tests, this smeared zone has a lower permeability than the original soil, which results in a slower rate of settlement, i.e., a longer settlement period.  In real life, however, even the most conscientious test programs indicate consolidation rates which may vary by factors of 3 or more.  The smear effect is simply not very significant, given this level of uncertainly in the design values.