Test: Soil Compaction - Civil Engineering (CE) MCQ

• Frog hammers are used to compact soils in confined areas and at corners e.g., back of retaining wall, etc.
• Soil densification techniques are used for reducing liquefaction hazards is to avoid large increases in pore water pressure during earthquake shaking.
• Vibrofloatation involves the use of a vibrating probe that can penetrate granular soil to depths of over 100 feet.
• The vibrations of the probe cause the grain structure to collapse thereby density the soil surrounding the proble.
• To treat area of potentially liquefiable soil, the vibroflot is raised and lowered in a grid pattern.

The effect of increasing the amount of compactive effort is to increase the maximum dry density and to decrease the optimum water content.

Max dry density is achieved after the suitable compaction method at certain moisture content.

Vibroflotation is most suitable for very loose sands submerged under water table. Efficiency of densification reduces with increase in silt and clay content and penetration rate reduces in case of dense sands with deep water tables.

Cohesionless soils can be compacted by vibration; flooding and dropping heavy weight from height. Kneading and tamping actions provided by sheeps foot roller and tandem roller are not effective for cohesionless soils.

Unit weight at zero air void corresponds to dry density of soil.

∴ it depends on specific gravity, water content and unit weight of water.

For a given type of compaction, the higher the compactive effort, the higher the maximum dry unit weight and lower the optimum moisture content.

With increase in compactive effort, the optimum moisture content decrease and dry density increases. Thus soil is to be compacted on the dry side of the optimum moisture content of original (lower compactive effort) Proctor curve.