During compaction the quantity of water at which the maximum density is obtained is known as:
Try it first: pick an option, then read the explanation.
Correct answer: D. Optimum moisture content
Asked in SSC JE 2016
Detailed Explanation
For a given compactive effort, adding water first increases the dry density and then decreases it. The water content at the turning point is special enough to have its own name.
Why “Optimum moisture content” Is Correct
That water content is called the optimum moisture content (OMC). If the compactive effort is increased, the soil reaches a higher dry density at a lower OMC.
Why the Other Options Are Wrong
- A. Half saturated soil: ‘Half saturated soil’ is not a defined state; at the OMC the degree of saturation is usually 80–90%.
- B. Water content: ‘Water content’ is the general term for any moisture; it does not identify the special value at maximum density.
- C. Saturated soil: Soil at the OMC is not fully saturated; some air voids remain.
Key Point
OMC is always tied to a particular compactive effort.
Key Concepts for Students
- OMC is read from the peak of the Proctor compaction curve.
- Compacting dry of OMC gives a stiffer, more permeable soil; wet of OMC gives a more flexible, less permeable soil.
- Field water content is controlled around the OMC before rolling.
Practice more: this is question 11 of Compaction of Soil MCQs – Part 2. Try the whole set and check every answer instantly.