Which of the following type of roller is most suitable for proof rolling subgrades and for finishing operation of fills with clayey or sandy soils?
Try it first: pick an option, then read the explanation.
Asked in SSC JE 24/01/2018 (Evening)
Detailed Explanation
Different rollers do different jobs within the same project. Sheep-foot or vibratory rollers do the heavy densification of each layer. The final pass, which leaves a smooth, sealed surface and checks the subgrade for soft spots, is a different task.
Why “Smooth wheel roller” Is Correct
A smooth-wheeled (steel drum) roller presses the top of the layer flat, seals the surface so rain runs off instead of soaking in, and reveals weak spots that deflect under the roller during proof rolling. That is why it is the standard choice for proof rolling subgrades and finishing fills of clayey or sandy soil.
| 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. Pneumatic rubber tired roller: Pneumatic rollers compact a wide range of soils and can also be used for proof rolling, but the classic answer for finishing operations is the smooth-wheeled roller.
- B. Sheepfoot roller: Sheep-foot rollers leave the surface full of foot impressions; they are for compacting clay layers, not finishing.
- D. Vibratory roller: Vibratory rollers are for densifying granular layers, not specifically for finishing clayey fills.
Key Point
Smooth-wheeled roller = finishing and sealing surfaces, proof rolling, crushed rock and gravel.
Key Concepts for Students
- Static smooth-wheeled rollers are 8–12 t; 3-wheel and tandem types are common.
- Their effective depth is small, so they are not used for thick loose lifts.
- Sealing the surface at the end of the day protects fills from rain.
Practice more: this is question 7 of Compaction of Soil MCQs – Part 2. Try the whole set and check every answer instantly.