soil compaction

CE 353 Geotechnical Engineering
Dr M. Touahmia

6

Soil Compaction

Lecture Outline:

1.
2.
3.
4.
5.
6.
7.

General Principles
Standard Proctor Test
Factors Affecting Compaction
Modified Proctor Test
Field Compaction
Measurement of Field Compaction
Special Compaction Techniques

Textbook: Braja M. Das, "Principles of Geotechnical Engineering", 7th E. (Chapter 6).

1

General Principles
What is compaction?
• Many types of earth construction, such as roads, railways, embankments, retaining walls, earth dams, and airport, require man-placed soils, or fills.
These soils are loose (weak) and must be compacted to increase their strength characteristics.
• Soil compaction is defined as the method of mechanically increasing the density of soil by reducing volume of air.

2

General Principles
• The densification is accomplished by pressing the soil particles together into a close state of contact with air being expelled from the soil mass in the process, thereby increasing its unit weight.
• The degree of compaction is measured in terms of the dry unit weight (γd).
• For a given water content (w), the maximum degree of compaction that can be achieved is when all of the air voids have been removed.
• The dry unit weight correlates with the degree of packing of the soil grains:

G
 
1 e s w

d

• The smaller the void ratio (e) will be, the higher the dry unit weight (γd) will be. 3

General Principles
Objectives of Compaction:
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1.
2.
3.
4.

Compaction is done to improve the Engineering properties of soil such as:
Increasing the shear strength of soil (i.e., larger loads can be applied).
Decreasing future settlements.
Reducing the compressibility of soil.
Decreasing permeability.

Affecting Factors
• There are 4 control factors affecting the extent of compaction:
1.
2.
3.
4.

Compaction effort.
Soil type and gradation.
Moisture content.
Dry unit weight (dry density).
4