Q.49 For field compaction of soil, in cohesive soil the combination of tamping action and kneading action on soil is achieved by:
- Apneumatic-tyred rollers
- Bvibroflotation
- Csheep foot rollersCorrect
- Dfrog rammers
Solution
Concept
A sheepsfoot roller compacts cohesive soil by tamping (feet press into soil) and kneading (feet move and remould soil).
Step-by-step solution
1. Note the soil type. It is cohesive soil (clay). 2. Note the action needed: tamping plus kneading. 3. A sheepsfoot roller has many projecting feet on its drum. 4. The feet push into the soil (tamping) and remould it as the drum rolls (kneading). 5. So the answer is sheepsfoot roller, option (C).
Explanation
A sheepsfoot roller has many feet fixed on a steel drum. The feet go deep into clay and press it (tamping), and they also mix and remould the soil (kneading). So it is the best roller for cohesive soils.
Why the other options are wrong
(A) Pneumatic-tyred rollers mainly give kneading and static pressing, not tamping by feet. (B) Vibroflotation is a deep vibration method for loose cohesionless (sandy) soils. (D) Frog rammers give impact (ramming) in small or confined areas, not combined tamping and kneading.
Shortcut
Clay = sheepsfoot roller; sand = vibratory roller; mixed soils = pneumatic roller.
Common mistake
Choosing pneumatic-tyred roller because it also gives kneading action, but it does not give tamping.
Correct answer: C) sheep foot rollers