(a)What are the purposes of the soil classification? (b) Explain the various factors affecting compaction.

  (a)What are the purposes of the soil classification? 

The purposes (objectives)of soil classification are:

➡️ To arrange various types of soils into groups according to their engineering or agricultural properties.

➡️To decide the suitability of soil as a construction material for the construction of the roads, earthen dams, embankments, etc.

➡️To decide the suitability of a soil for the foundation of the structures.

➡️ A soil classification system is provides a common language between engineers dealing with soils. It is useful in exchange of information and experience between the geotechnical engineers. 

(b)Explain the various factors affecting compaction.

The important factors affecting compaction are,

(1)Water content

(2)Amount of compaction

(3)Type of soil

(4)Method of compaction

(5)Thickness of lyer

(6)Saturation line

(7)Admixtures

(8)Stone content

(1)Water content

      At low water content, the soil is stiff and offfer more resistance to compaction. As the water content is decreased, the soil particle get lubricated. The soil mass becomes more workable and the particles have closer packing.

   The dry density of soil increases with an increase in water content til the optimum water content is reached. At that stage, the air voids attain approximately a constant volume. With further increase in water content, the air voids don't decrease, but the total voids (air+water) increase and the dry density decreases.

(2)Amount of compaction

    The amount of compaction greatly affects the maximum dry density and optimum moisture content of a given soil. The effect of increasing the compactive energy result in an increasing the compative energy result in an increase in maximum dry density and decrese in optimum moisture content. However, the increase in MDD does not have a linear relationship with increase of compactive effort.

(3)Type of soil

    The maximum dry density achieved depends upon the types of the soil. In general coarse grained soils can be completed to higher dry density than fine grained soils. A well graded sand attains a much higher dry density than a poorly graded soil. Cohesive soils have high air voids. These soils attain relatively lower maximum dry density as compared with the cohesionless soils.

(4)Method of compaction

   The dry density achieved also depends upon the method of compaction. For the same amount of compactive effort, the dry density will depends upon the whether the method of compaction utilizes kneading action, dynamic action or stationary action.

(5)Thickness of layer  

  In the compaction of soils the thickness of soil layer also play an important role. Normally the thickness of layer in laboratory is kept 30 to 40 mm, while in the field the thickness of soil layer is kept about 200 to 300 mm. The lesser thickness of soil layer gives higher dry density.

 

(6)Saturation line

  If all the air voids are removed from the soil by compaction, the soil becomes fully saturated and higher maximum dry density is achieved. Therefore, saturation below 100% results in lower maximum dry density. Practically 100% saturation is not possible.

(7)Admixtures

  The compaction characteristics of the soils are improved by adding some admixtures. The most commonly used admixtures are lime, cement and bitumen.

(8)Stone content

  With addition of aggregrates of 20 to 30 mm size up to 40% volume, the density of soil increases.

I hope that you have understand various factors affecting compaction theory very well.