We know soil loose its strength under remolding. The term thixotropy is related to remolding. The strength loss is due to
-alteration of soil structure
-disturbance of water molecules that were in adsorbed condition
But this change in remolding is not one way. Sometimes this alternation are observed reversible. If such soil is allowed to rest unaltered in respect of water loss, it is observed that it regains strength to some extent. In geotechnical engineering, gaining of strength of soil with course of time after it get remolded is known as thixotropy.
Thixis stand for touch
Tropo stand for change
That is thixotropy means changes that happened under agitation or touch.
The gaining in strength is due to
-gradual reorientation of water molecules in layers of adsorbed water
-a regaining of the chemical equilibrium
This phenomena have great importance in practical field of geotechnical engineering.
As an example: In case of driven pile, a loss of strength occurs as a result of disturbance due to vibration of driving. Thixotropy in this case defined by gaining of shear strength after driving disturbance when piles are left for some duration.