Effect of compaction on soil properties

1. Soil structure :-

The water content at which the soil compacted plays an important role. Soil compacted at a water level less than the optimum water content generally have a flocculated structure, regardless of the method of compaction. soil compacted at the water level more than the optimum water content generally have a dispersed structure. If the compaction induces large shear strains and a flocculated structure if the shear are relatively small.

2. Permeability :-

When the compaction effort increased , the permeability of the soil is decreased due to increased dry density and better orientation of particles because the permeability of soil depends upon the size of voids. The permeability of soil decrease with an increase in water content on the dry side of the optimum water content. There is an improved orientation of the particles and a corresponding reduction in the size of voids. The minimum permeability occurs at or slightly increases, but permeability always remains much less than that on the dry side of the optimum. The slight increase in the permeability take place due to the effect of a decrease in the dry density.

3. Shrinkage :-

Soil compacted dry of the optimum shrink less on drying compared with those compacted wet of the optimum. The soil compacted wet of the optimum shrink more due to the soil particles in the dispersed structure have nearly parallel orientation of particle and can pack more efficiently.

 4. Compressibility :-

The compressibility of compacted soil varies according to the amount of pressure applied.

For low pressure range, compressibility is more for soil which are compacted to wet of optimum than soil compacted to dry of optimum.

For high pressure range, compressibility is more for soil which are compacted to dry of optimum than soil compacted to wet of optimum.

5. Swelling :-

when soil is compacted dry of optimum water content, the soil particles orientated in random manner due to which it swells easily when it come  in contact with water. 

when the soil is compacted wet of optimum water content, the soil particles orientated in disperse manner and swelling not occur.

Thus to avoid swelling soil is to be compacted to the wet of optimum water content.

6. Pore water pressure :-

Pore water pressure high for the soil whose water content is high. Thus the soil compacted to the wet of optimum water content will have high pore water pressure than the soil compacted dry of optimum water content.

7. Stress-strain relationship :-

Soil compacted to dry side of optimum will take stress for little strain hence, stress-strain curve of this type of soil is steeper than those on wet side.

The strength and modulus of elasticity of soil on dry side of optimum will be high.

soil compacted dry of optimum shows brittle failure and soil compacted on wet side experience increased strain.

8. Shear strength :-

Shear strength of soil compacted to dry of optimum is more than those compacted to wet of optimum at lower strains. At higher strain, soil compacted to wet optimum will have more shear strength. Type of compaction, drainage conditions and type of soil also influence the shear strength of compacted soil.