Maximum bulking of sand occurs at a moisture content of approximately:
Correct Answer: B. 5%
📚 Detailed Explanation: Moisture Content for Maximum Bulking
Why B (5%) is correct: At very low moisture (~1–2%), film thickness is insufficient to significantly separate particles. As moisture increases to ~4–6%, films reach the optimal thickness for maximum surface tension effect → maximum particle separation → maximum bulking. Beyond ~6–8%, excess water fills the inter-particle voids, reducing the net surface tension effect and starting to decrease bulking. At saturation, no surface tension → zero bulking.
Bulking vs. Moisture Content
| Moisture (%) | Bulking | Reason |
|---|---|---|
| 0 | 0% | No water film |
| 2–3 | 10–20% | Thin films developing |
| 4–6 (~5%) | 20–35% (maximum) | Optimal film thickness for maximum surface tension |
| 8–10 | Decreasing | Excess water fills gaps |
| Saturated | ~0% | No surface tension effect |
- Maximum bulking occurs at approximately 5% (4–6%) moisture content.
- Fine sand bulks more (≈35%) than coarse sand (≈15%) at the same moisture level.