What is over-consolidation?

Answer 1

Think of a clay body like a sponge. When the sponge is wet it swells up and when a pressure is applied to the sponge, water is forced out and the sponge shrinks. Consolidation is the term used to describe this phenomenon in clays.

Normaly, the pressure applied to clays is due to the overburden pressure, or weight of the overlying clays bearing down on the strata. Therefore a normally consolidated clay is one that becomes more dense - that is more consolidated and tightly packed - as you go deeper into the strata.

Over consolidated clays occur when at some stage during the history of the deposit, other earth pressures have been applied resulting in more water being squeezed out than would normally be expected. This causes the clay to become more densely packed in and as such is over consolidated.

Over time, more clay is deposited over this layer resulting in normally consolidated clay over a denser layer of over consolidated clay...

pheeeew, this is the best I can explain it with out making you sick with an intense geotechnical filibuster.

Rohan