Sensitivity, Thixotropy & Activity | Properties of Soil | Soil Mechanics

Sensitivity

⇒Consistency (strength) of undisturbed samples of clay may change upon remoulding even at the same water content.

⇒This change in consistency or decrease in the degree of firmness or decrease in shear strength take place due to the following reasons.

1. Due to permanent destruction of soil solids up to remoulding (Due to breaking of intermolecular bonds Which is not recoverable).
2. Due to reorientation of water molecules in the adsorbed layer of soil solids (Recoverable).

⇒This loss in strength of soil in represented in terms of its ” SENSITIVITY” which signifies the degree of disturbance of soil sample upon remoulding.

⇒It is defined as the ratio of Unconfined Compressive Strength in an undisturbed natural state to Unconfined Compressive Strength of soil in the remoulded state.

\(s=\frac{\text{(ucs)Undisturbed}}{\text{(ucs)Remoulded}}\).

⇒It represents degree of disturbance archived on remoulding.

(Sensivitivity is the properties of soil at which soil loss the strength at same water content.)

Thixotropy

Over a period of time soil regains a part of its lost strength ( on the account of remoulding), (due to rehabilitation of water molecules in an adsorbed layer of soil to attain chemical equilibrium).

This property of soil by virtue of which it regains a part of its lost strength is termed thixotropy.

Higher the sensitivity of soil, the higher is its thixotropy hardening.

This property of soil plays an important role where construction activities involve the remoulding of natural clay deposits, Ex-Piling.

Cohesive soil has greater thixotropy than cohesion less soil.

Activity

The behaviour of plasticity of soil depends upon the type of mineral, amount of minerals & amount of water present in adsorbed layer of soil.

Skempton define a parameter termed as Activity, which represent the compressibility or volume change in soil with change in water content.

It is defined as ratio of plasticity index and percentage of the particles present in it having size less than 2μ (clay size).

\(A_t=\frac{I_p}{C}\).

C=% of particles finer than 2μ.

Note: Higher active soil are not suitable for constant activities (Because more volume change), Ex-Black cotton soil.

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