The maximum water content at which a reduction in the water content will not cause a decrease in the volume of soil mass is known as .........of soil sample.
Try it first: pick an option, then read the explanation.
Detailed Explanation
As a fine-grained soil dries out, it passes through several distinct states. Below a certain water content, further drying stops shrinking the soil any further — the particles have already packed as tightly as they can, and any remaining water loss is simply replaced by air entering the voids rather than the soil mass shrinking.
Why "shrinkage limit" Is Correct
The shrinkage limit (WS) is defined as exactly this: the water content below which any further reduction causes no further decrease in the total volume of the soil mass. At the shrinkage limit itself, the soil is still 100% saturated (every void is water-filled) — but drying below it simply lets air into the voids without any additional shrinkage.
| Limit | Boundary Between | How It's Tested |
|---|---|---|
| Liquid Limit (WL) | Liquid ↔ Plastic | Casagrande grooving-tool apparatus (25 blows) |
| Plastic Limit (WP) | Plastic ↔ Semi-solid | Rolling into a 3 mm thread until it crumbles |
| Shrinkage Limit (WS) | Semi-solid ↔ Solid | Mercury displacement volume test |
Key Point
At the shrinkage limit, degree of saturation is still exactly 100% — the soil isn't "dry" yet, it has simply stopped changing volume as it continues to dry.
Key Concepts for Students
- Below the shrinkage limit, the soil's total volume stays essentially constant even as its water content and weight continue to decrease.
- The shrinkage limit test uses mercury (see Q10/Q13) to precisely measure the dry volume of the soil pat, since mercury doesn't wet or stick to the soil the way water would.
- Shrinkage limit is the boundary between the semi-solid and solid states — it sits at the driest end of the consistency spectrum, opposite the liquid limit.
- Do not confuse the shrinkage limit with the plastic limit — the plastic limit is a wetter boundary (plastic ↔ semi-solid), not the driest one.