Sensitivity of Soil/ Clay : Formula, Diagram, Table
The ratio of unconfined compression strength of clay in the natural or undisturbed state to that in the remoulded state, without any change in the water content is called as sensitivity of soil.
A soil’s strength can be higher in its undisturbed state than in its disturbed remoulded state. Many cohesive soils fall into this category. This behaviour is referred to as soil sensitivity, which is described as the ratio of shear strength in the undisturbed state to that in the completely remoulded state.
When the strength of an undisturbed sample of clay is measured and then measured again after remoulding to the same dry density at the same water content, a decrease in strength is often observed. This is a significant phenomenon that can be quantified using the formula below.
Below figure shows a comparison of stress-strain curves for a sensitive clay in both the undisturbed and remoulded states.
Soil sensitivity can range from 1 to 100, so it’s divided into 7 categories: insensitive, sensitive, medium sensitive, extra sensitive, quick, medium quick and slightly quick. The sensitivity description is shown in the sensitivity of soil table below.
Also Read : Thixotropy of Clay (Soil Mechanics)
| Description | Sensitivity ‘St’ |
|---|---|
| Insensitive | < 2 |
| Medium Sensitive | 2 – 4 |
| Sensitive | 4 – 8 |
| Very Sensitive | 8 – 16 |
| Slightly Quick | 16 – 32 |
| Medium Quick | 32 – 64 |
| Quick | > 64 |
- Soil that has been deposited in a marine environment is usually very sensitive.
- The sensitivity of some quick clays will exceed 100.
- Soils that have been over-consolidated have been observed to be insensitive. This is partially due to the low natural water content in deposits of soil.
- Clays with a sensitivity greater than 8 should be treated with caution during construction because disturbance appears to turn them into viscous fluids. These clays are from the montmorillonite family and have a flocculent structure.