Soil Mechanics Questions and Answers – Sensitivity and Thixotropy of Clays

This set of Soil Mechanics Multiple Choice Questions & Answers (MCQs) focuses on “Sensitivity and Thixotropy of Clays”.

1. The consistency of an undisturbed sample of clay is altered, even at the same water content, if it is remoulded.
a) True
b) False

Explanation: The consistency of an undisturbed sample of clay is altered because the original structure of clay is altered by reworking or remoulding.

2. Remoulding of clay results in _______
a) increase in its strength
b) decrease in its strength
c) no change
d) decrease in compressibility

Explanation: The strength of a clay soil is related to its structure. Due to the destruction of the clay particle structure that was developed during the original process of sedimentation, there is loss of strength of clay soils.

3. The degree of disturbance of undisturbed sample of clay due to remoulding is expressed by______
a) activity of clay
b) sensitivity
c) thixotropy
d) density index

Explanation: The activity of clay is related with the plasticity and the quantity of clay-size particles. Thixotropy is the phenomenon of ‘strength loss – strength gain’. The density index is used to express the relative compactness.

4. Sensitivity is defined as _____
a) Ip/CW
b) qu(undisturbed) / qu(remoulded)
c) Vv/VS
d) Ww/Wd

Explanation: The Sensitivity is defined as the ratio of unconfined compressive strength in natural state to that in remoulded state.
St = qu(undisturbed) / qu(remoulded)

5. The sensitivity of honey comb structure of clay is ______
a) 1
b) 8 to 16
c) 2 to 4
d) greater than 16

Explanation: The classification of clays based on sensitivity is given by,

 Sensitivity Structure 1 – 2 to 4 Honey comb structure 4 to 8 Honey comb or Flocculent structure 8 to 16 Flocculent structure >16 Unstable

6. The Thixotropy is the phenomenon of _______
a) strength loss
b) strength gain
c) strength loss – strength gain
d) strength gain – strength loss

Explanation: When sensitive clay is used in construction, it loses its strength due to remoulding and with passage of time they regain their strength though not to original level. The phenomenon of ‘strength loss – strength gain’ with no change in water content or volume is termed as Thixotropy.

7. The larger the sensitivity, ______ the thixotropy hardening.
a) smaller
b) no change in
c) lower
d) larger

Explanation: Sensitivity is the degree of disturbance due to ‘remoulding’ and the thixotropy is the process of softening of clay due to ‘remoulding’, followed by time-dependent gain in strength. So, it can be said that they are directly proportional to each other.

8. The gain in strength after remoulding is due to______
a) permanent destruction of structure
b) reorientation of molecules
c) rehabilitation of molecular structure
d) crystallization

Explanation: The loss of strength is due to permanent destruction of structure and reorientation of molecules of clay. The gain in strength is due to rehabilitation of molecular structure of the soil.

Sanfoundry Global Education & Learning Series – Soil Mechanics.