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Soil Compaction For Construction | Factors Affecting of Soil Compaction

Soil Compaction

Today we discuss Soil Compaction For Construction with Soil Compaction Definition, different Factors Affecting Compaction of soil in geotechnical engineering in the civil experience blog

Soil Compaction Definition

Soil Compaction Definition
In geotechnical engineering, soil compaction is the process in which stress applied to a soil causes densification as air is displaced from the pores between the soil grains.

Now we look on What is the reason for soil compaction for construction?

Reason for Soil Compaction

  • To increase the bearing capacity of the soil we carried out soil compaction for construction. (Compaction of concrete)
  • Soil Compaction also is used to reduce the void ratio and make the soil compacted to bear the soil load of the external structure as you remove voids you decrease the chance of settlement.
  • Compaction is to consolidate the soil so that no further settlement would occur when the building is built.

Factors Affecting Soil Compaction For Construction

Various factors affecting the compaction of soil but here we learn four main factors which influence compaction and they are as follows:

Water Content Factors Affecting Soil Compaction

There are two theories to explain the typical water content-dry unit weight relationship.

  1. Lubrication theory by Proctor
  2. Electrical Double Layer theory by Lambe.

πŸ‘‰ According to Lubrication theory at lower water contents, the soil is stiff and the soil grains offer more resistance to compaction.

πŸ‘‰ As the water content increases, the dry density increases and air voids are decreased till the optimum water content is reached, a stage when the lubrication effect is maximum.

πŸ‘‰ However, the water starts to replace the soil particles with a further increase in moisture content, and since Ξ³w < < Ξ³s, the dry unit weight starts decreasing.

πŸ‘‰ Lambe uses the concept of soil structure and the Electrical Double Layer theory to explain the effect of water content on dry unit weight.

πŸ‘‰ In case of cohesive soils, there is an attractive force namely the Van-der Waal’s forces which acts between two soil particles and a repulsive force which is due to double layers of adsorbed water tending to come into contact with each other.

πŸ‘‰ While the attractive forces remain the same in magnitude, the repulsive force is directly related to the size of double layers.

πŸ‘‰ If the net force between the particles is attractive, the flocculated structure is the result; if it is repulsive, the particles tend to move away 'disperse'.

πŸ‘‰ At low water contents, attractive forces are predominant, making it difficult for the particles to move about when compactive effort is applied.

πŸ‘‰ Low dry unit weight is the consequence. As the water content is increased, the double layer expands and inter particle repulsive forces increase.

πŸ‘‰ The particles easily slide over one another and get packed more closely, resulting in higher dry unit weight.

πŸ‘‰ The maximum expansion of the double layer is at the OMC, beyond that, the addition of water does not add any further to the expansion of the double layer but the water tends to occupy space that otherwise would have been occupied by soil particles.

πŸ‘‰ Hence a decrease in unit weight. It also explains why the shape of the compaction curve is not the typical inverted V shape in the case of soils that are not cohesive and plastic in nature.

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Compactive Effort

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

Soil Compaction For Construction | Factors Affecting of Soil Compaction
Soil Compaction For Construction

πŸ‘‰ In the above figure compaction curve B corresponds to the higher compactive effort in a MPT, comparing it with the compaction curve A for SPT, one can see the compaction curve shifts to the top and to the left when compactive effort is increased.

πŸ‘‰ However, the margin of increase becomes smaller and smaller even on the dry side of the OMC while on the wet side of OMC, there is hardly any increase at all.

πŸ‘‰ If the peaks of compaction curves for different compactive efforts are joined together a ‘line of optimums’ is obtained which is nearly parallel to zero air void line.

πŸ‘‰ This brings out the fact that even a higher compactive effort does not result in a higher efficiency of compaction.

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Types of Soil

(a) Coarse grained, well graded soils compact to high dry unit weight especially if they contain some fines.

(b) Poorly graded sands lead to the lowest dry unit weight values.

(c) In clay soils, the maximum dry unit weight tends to decrease as plasticity increases.

(d) Cohesive soils have generally high values of OMC.

(e) Heavy clays with high plasticity have very low maximum dry density and very high OMC.

Methods of Compaction

πŸ‘‰ Ideally speaking, the laboratory test must reproduce a given field compaction procedure, because the mode of compaction does influence somewhat the shape and the position of the 'Ξ³d' vs ‘w' plot.

πŸ‘‰ Since the field compaction is essentially kneading type compaction or rolling type compaction and the laboratory tests use the dynamic impact type compaction, one must expect some divergence in the OMC and Ξ³d max in the two cases

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FAQ 1:  What is the Soil Compaction Definition?

 Soil Compaction Definition is In geotechnical engineering, soil compaction is the process in which stress applied to a soil causes densification as air is displaced from the pores between the soil grains.

FAQ 2:  What are the Reason for Soil Compaction?

1. To increase the bearing capacity of the soil we carried out soil compaction for construction2. Soil Compaction also is used to reduce the void ratio and make the soil compacted to bear the soil load of the external structure as u remove voids you decrease the chance of settlement.3. Compaction is to consolidate the soil so that no further settlement would occur when the building is built.

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