The optimum water content (OWC) is the moisture content at which the soil attains ______.
Try it first: pick an option, then read the explanation.
Asked in SSC JE 10/10/2023 (Morning)
Detailed Explanation
For a fixed compactive effort, dry density first increases as water is added (water lubricates the particles so they slide closer together), reaches a peak, and then decreases (extra water starts occupying space that solids could have filled). The water content at the peak is called the optimum water content (OWC) or optimum moisture content (OMC).
Why “maximum dry density” Is Correct
‘Optimum’ means the best water content for compaction, and ‘best’ is measured by the dry density achieved. So the OWC is, by definition, the water content at which the soil reaches its maximum dry density under that compactive effort.
Why the Other Options Are Wrong
- B. maximum water content: Water content can keep increasing beyond the OMC; the OMC is not a maximum of water content.
- C. minimum dry density: Minimum dry density is not associated with an optimum; dry density is lowest at the ends of the curve.
- D. fully saturated density: At the OMC the soil is not fully saturated; some air voids (about 2–5%) remain.
Key Point
OMC depends on the compactive effort: more effort gives a lower OMC and a higher MDD.
Key Concepts for Students
- Clays have higher OMC (roughly 15–30%) than sands (roughly 8–12%).
- Compacting on the dry side gives a flocculated, stiffer, more permeable structure; on the wet side a dispersed, more flexible, less permeable structure.
- Field water is adjusted to around OMC (often within ±2%) before rolling.
Practice more: this is question 7 of Compaction of Soil MCQs – Part 1. Try the whole set and check every answer instantly.