Which of the following types of soil have excellent workability as a construction material?
Correct Answer: A. Well graded gravel
📚 Detailed Explanation: Soil Workability in Construction
In geotechnical engineering, “workability” of soil as a construction material refers to how easily the soil can be excavated, transported, placed, and compacted to form stable embankments, fills, or subgrades.
Why A (Well graded gravel) is correct: Well-graded gravel (GW per USCS) has a wide range of particle sizes that interlock and compact efficiently. It: (1) drains freely (non-plastic, not frost-susceptible); (2) is easy to compact with standard equipment; (3) develops high shear strength; (4) does not swell/shrink. Silty sand (SM) and clayey sand (SC) have cohesive fines that make compaction sensitive to moisture and create shrinkage/swelling issues. Silty gravel (GM) is intermediate but the silt fraction introduces some problem behaviour.
USCS Soil Workability for Construction
| Soil Type | USCS Symbol | Construction Workability |
|---|---|---|
| Well graded gravel | GW | Excellent |
| Silty gravel | GM | Good |
| Silty sand | SM | Fair (frost-susceptible) |
| Clayey sand | SC | Poor (shrink/swell) |
- Well-graded gravel = best construction material due to free drainage, easy compaction, and high stability.
- Fine-grained soils (silty, clayey) = poor workability due to moisture sensitivity and volume change.