Quick clay has a remolded strength which is much less than its strength upon initial loading. This is caused by its highly unstable clay particle structure.
Quick clay is originally deposited in a marine environment. Clay mineral particles are always negatively charged because of the presence of permanent negative charges and pH dependent charges at their surface. Because of the need to respect electro-neutrality and a net zero electrical charge balance, these negative electrical charges are always compensated by the positive charges born by cations (such as Na) adsorbed onto the surface of the clay, or present in the clay pore water. Exchangeable cations are present in the clay minerals interlayers and on the external basal planes of clay platelets. Cations also compensate the negative charges on the clay particle edges caused by the protolysis of silanol and aluminol groups (pH dependent charges). So, clay platelets are always surrounded by an electrical double layer (EDL), or diffuse double layer (DDL). The thickness of EDL depends on the salinity of water. Under salty conditions (at high ionic strength) EDL is compressed (or said to be collapsed). It facilitates the aggregation of clay platelets which flocculate and stick together in a more stable aggregates structure. After the marine clay deposit is uplifted and is no longer exposed to salt water conditions, rainwater can slowly infiltrate the poorly compacted clay layer and the excess of NaCl present in seawater can also diffuse out of the clay. As a result, the EDL is less compressed and can expand. It results in a stronger electrostatic repulsion between negatively charged clay platelets which can more easily become dispersed and form stable suspensions in water (peptization phenomenon). The effect leads to a destabilization of the clay aggregates structure.
In case of insufficient mechanical compaction of the clay layer, and with a shear stress, the weaker EDL compression by the salts in the quick clay results in clay particle repulsion and leads to their realignment in a structure that is weaker and unstable. Quick clay regains strength rapidly when salt is again added (compression of the EDL), which allows clay particles to restore their cohesion with one another.