Various factor which effect soil compaction | Factor effecting compaction of soil | Various factor effecting compaction of soil

 1. Water content :-

At low water content, the soil is stiff and offer high resistance to compaction. As the water content is increased, the soil particles get lubricated. The soil mass becomes more workable and the particles have close packing.

The dry density of the soil increases with an increase in the water content till the optimum water content in reached. At that stage, the air voids attain approximately a constant volume. With further increase in water content, the air voids do not decrease, but the total voids (air plus water) increase and the dry density decrease.

Thus the higher dry density is achieved up to the optimum water content due to forcing air voids out from the soil voids. After the optimum water content is reached, it becomes more difficult to force air out and to further reduce the air voids.

The electrical double layer theory also help to explain the effect of water content on the dry density of soil. At lower water content, the attraction forces in the absorbed water layer are large, and their is more resistance to movements of the particles. As the water content is increased, the electric double layer expends and the interparticle repulsive force increase. Now, the particles easily slide over one another and are closely packed. this result in higher dry density.

2. Method of compaction :-

The dry density achieved depends not only upon the amount of combative effort but also on the method of compaction. For the same amount of compactivity effort, the dry density will depend upon whether the method of compaction utilizes kneading action, dynamic action or static action.

For example, in Harvard miniature compaction test, the soil is compacted by the kneading action, and therefore, the compaction curve obtained is different from that obtained from the other conventional tests in which an equal compactivity effort is applied.

different method of compaction give their own compaction curve. The lines of optimum are also different, consequently.

3. Types of soil :-

The dry unit weight obtained depends upon the type of soil. Figure shows the optimum water content and the maximum dry density for different soil. Usually, coarse grain soils can be compacted to higher dry density than fine grained soils. With the addition of even a small quantity of fines to a coarse grained soil, the soils attain a much higher dry density for the same compactive effort. 

however, if the quantity of the fines is increased to a a value more than that required to fill the void of the coarse grained soils, the maximum dry density decrease. A well graded sand attains a much higher dry density than a poorly graded soil.

cohesive soil have high air voids. These soils attain a relatively lower maximum dry density as compared with the cohesionless soils, Such soils require more water than cohesionless soils and therefore the optimum water content is high. Heavy clay of very high plasticity have very low dry density and a very high optimum water content.

4. Amount of compaction :-

The effect of increasing the amount of compactive effort is to decrease the optimum water content and to increase the maximum dry density as shown in figure. the effect of increased compaction is more predominant when the water content is less than the optimum. If water content is more than the optimum, the air voids volume becomes almost constant and the effect of increased compaction is not significant.

It may be mentioned that the maximum dry density does not go on increasing with an increase in the compactive effort, the increase in the dry density with an increase in the compactive effort.

The line of optimum which follows the general trends of the zero-air void line for joining the peak of the compaction curve of different compactive effort. This corresponds to air voids of about 5%.