After compacting the subgrade, by suitable methods, the tests to ensure that the desired compaction has been achieved is/are:
- Amoisture content and field density determination testCorrect
- Bconsolidation test
- Ccompaction test and triaxial shear test
- Ddirect shear test
Solution
Concept
Field compaction is checked by measuring the field dry density and moisture content and comparing them with the lab MDD and OMC.
Formula
γd = γ / (1 + w); Relative compaction = (γd field / γd max) × 100
Step-by-step solution
1. After rolling, we must check if the subgrade reached the required density. 2. Find field moisture content (oven dry, rapid moisture meter, etc.). 3. Find field density (sand replacement or core cutter method). 4. Calculate field dry density γd = γ / (1 + w). 5. Compare with lab maximum dry density to get relative compaction. 6. So the tests needed are moisture content and field density tests. Answer (A).
Explanation
Compaction control in the field is done by finding the dry density achieved at the site. For this we need the field density and the moisture content. Tests like consolidation or shear tests are not used for routine compaction control.
Why the other options are wrong
B: Consolidation test gives settlement properties, not field compaction. C: Compaction test is a lab test that gives MDD and OMC. Triaxial test gives shear strength. Neither checks field compaction. D: Direct shear test gives shear strength parameters, not compaction achieved.
Shortcut
Field compaction check = field density + moisture content (sand replacement or core cutter).
Common mistake
Choosing the lab compaction (Proctor) test, which only sets the target and does not check the field work.
Correct answer: A) moisture content and field density determination test