Which of the following roller is used to compact the coarse-grained soil?
Try it first: pick an option, then read the explanation.
Correct answer: D. Vibratory roller
Asked in SSC JE 27/01/2018 (Morning)
Detailed Explanation
Coarse-grained soils such as sands and gravels have little or no cohesion. Static pressure or tamping does not rearrange their grains effectively; vibration does.
Why “Vibratory roller” Is Correct
A vibratory roller shakes the grains so that inter-particle friction is momentarily overcome and the grains settle into a denser packing. It is widely used for sub-base and subgrade layers of roads, embankments and dam shells built of granular material.
| Equipment | Best suited for | How it compacts |
|---|---|---|
| Smooth-wheeled (static) roller | Crushed rock, gravel; finishing surfaces; proof rolling subgrades | Static pressure |
| Pneumatic-tyred roller | Sands, gravels, silts and clayey soils (not uniformly graded soils) | Pressure + kneading |
| Sheep-foot roller | Clays and silty clays (cohesive soils) | Tamping + kneading |
| Vibratory roller | Sands and gravels (cohesionless soils) | Vibration |
| Rammers / frog hammer | Confined areas, trenches, near structures | Impact |
Why the Other Options Are Wrong
- A. Drum roller: A plain (static) drum roller compacts only a thin top layer of loose granular soil.
- B. Pneumatic tyred roller: Pneumatic rollers can be used on many soils, but they are not the most effective choice for coarse-grained soil.
- C. Tamping roller: Tamping (sheep-foot type) rollers are meant for cohesive soils such as clay.
Key Point
Coarse-grained → vibratory roller. Fine-grained/clay → sheep-foot (tamping) roller.
Key Concepts for Students
- Vibration frequency is chosen near the natural frequency of the soil for best results.
- Lift thickness for vibratory rollers can be larger than for static rollers.
- Over-vibration of saturated fine sands can cause temporary loss of strength.
Practice more: this is question 6 of Compaction of Soil MCQs – Part 2. Try the whole set and check every answer instantly.