Compaction of Soils Questions and Answers

Answer: B

The vibratory roller is used for Well graded dry sand.

Vibration rearranges the grains of cohesionless soils such as sands and gravels into a denser packing, so vibratory rollers are the most effective compactors for granular material, especially well-graded sand.

Clays and silts are cohesive; their particles are held by water films and are compacted better by kneading and pressure, with sheepsfoot or pneumatic-tyred rollers. Moist silty sand also responds less well to vibration than clean sand.

Answer: D

Greater compactive effort gives an increase in maximum dry density and decrease in OMC.

Heavier compaction, as in the modified Proctor test compared with the standard test, pushes the particles closer together, so the soil reaches a higher maximum dry density. Because the extra energy does part of the work that water does as a lubricant, that peak is reached at a lower water content. The compaction curve moves upward and to the left, along the line of optimums.

So the maximum dry density does change, ruling out option A, and the optimum moisture content falls, ruling out B and C.