Q.25 Which of the following types of soil have excellent workability as a construction material?
- AWell graded gravelCorrect
- BClayey sand
- CSilty sand
- DSilty gravel
Solution
Concept
In the Unified Soil Classification System (USCS) table of engineering properties, well graded gravel (GW) has excellent workability as a construction material.
Step-by-step solution
1. Recall the USCS table of soil groups and their properties for construction. 2. GW (well graded gravel): workability excellent. 3. GM (silty gravel): workability good. 4. SM (silty sand) and SC (clayey sand): workability fair. 5. So the best answer is well graded gravel.
Explanation
Well graded gravel has a good mix of all particle sizes. It is easy to place, spread and compact, and it drains well. So its workability as a construction material is rated excellent.
Why the other options are wrong
B: Clayey sand has fair workability because the clay makes it sticky. C: Silty sand has fair workability and is sensitive to water. D: Silty gravel has good, not excellent, workability.
Shortcut
Coarse, clean and well graded soil (GW) gives the best workability. Fines like silt and clay reduce it.
Common mistake
Choosing silty gravel just because it is also gravel. The silt fines lower its rating to good.
Correct answer: A) Well graded gravel