Optimum moisture content is obtained from?
Try it first: pick an option, then read the explanation.
Correct answer: B. standard proctor test
Asked in SSC JE 2016
Detailed Explanation
The optimum moisture content is a property of compaction, so it must come from a compaction test. The standard Proctor test compacts the soil at several water contents and plots dry density against water content; the peak gives MDD and OMC.
Why “standard proctor test” Is Correct
Only the Proctor (light or heavy) compaction test produces the compaction curve from which the OMC is read. In the field, the soil is brought to about this water content before rolling.
Why the Other Options Are Wrong
- A. hydrometer test: The hydrometer test gives the particle size distribution of fine soils (silt and clay sizes).
- C. consolidation test: The consolidation test gives compressibility and rate of settlement (Cc, mv, cv).
- D. triaxial test: The triaxial test gives shear strength parameters (c, φ) under controlled drainage.
Key Point
OMC + MDD → Proctor compaction test; in-situ density → core cutter or sand replacement.
Key Concepts for Students
- IS 2720 Part 7 = light compaction; Part 8 = heavy compaction.
- At least 5 points are usually plotted to define the peak well.
- The test is done on soil passing the 20 mm (or 4.75 mm) sieve, depending on the mould.
Practice more: this is question 9 of Compaction of Soil MCQs – Part 2. Try the whole set and check every answer instantly.