Which of the following is NOT correct about the effects of compaction of soil?
Try it first: pick an option, then read the explanation.
Asked in SSC JE 29/10/2020 (Morning)
Detailed Explanation
Compaction expels air and reduces the volume of voids. Almost every engineering benefit follows from this: denser soil is stronger, stiffer and settles less. Flow of water, however, depends on the size and connectivity of voids.
Why “Compaction increases the permeability of soil” Is Correct
Because compaction makes the voids smaller and fewer, water finds it harder to flow through the soil. Permeability therefore decreases. The statement that compaction increases permeability is the incorrect one. (Clay cores of earth dams are compacted precisely to make them less permeable.)
Why the Other Options Are Wrong
- A. Compaction increases shear and bearing strength of soil: Correct effect: denser packing increases interlocking and friction, raising shear strength and bearing capacity.
- C. Compaction increases the frictional characteristics of soil: Correct effect: closer particle contact improves frictional resistance.
- D. Compaction decreases the tendency for settlement of soil: Correct effect: with fewer voids left to close, later settlement under load is reduced.
Key Point
Compaction ↑ density, strength, bearing capacity, stability. Compaction ↓ voids, permeability, compressibility, settlement.
Key Concepts for Students
- Clay compacted dry of optimum is more permeable than the same clay compacted wet of optimum.
- Reduced permeability also lowers seepage and frost susceptibility.
- Over-compacting some clays can increase swelling potential.
Practice more: this is question 3 of Compaction of Soil MCQs – Part 2. Try the whole set and check every answer instantly.