compaction
COMPACTION
Compaction is the application of mechanical energy to a soil to rearrange the particles and reduce the void ratio.
1 Purpose of Compaction :
• The principal reason for compacting soil is to reduce subsequent settlement under working loads.
• Compaction increases the shear strength of the soil.
• Compaction reduces the voids ratio making it more difficult for water to flow through soil. This is important if the soil is being used to retain water such as would be required for an earth dam.
• Compaction can prevent the build up of large water pressures that cause soil to liquefy during earthquakes.
2 . Factors affecting Compaction
• Water content of the soil
• The type of soil being compacted
• The amount of compactive energy used
3. Field specifications :
To control the soil properties of earth constructions (e.g. dams, roads)
it is usual to specify that the soil must be compacted to some pre-determined dry unit weight.
This specification is usually that a certain percentage of the maximum dry density, as found from a laboratory test (Standard or Modified) must be achieved.
For example we could specify that field densities must be greater than 98% of the maximum dry unit weight as determined from the Standard Compaction Test.
It is then up to the Contractor to select machinery, the thickness of each lift (layer of soil added) and to control moisture contents in order to achieve the specified amount of compaction.
Compaction is the application of mechanical energy to a soil to rearrange the particles and reduce the void ratio.
1 Purpose of Compaction :
• The principal reason for compacting soil is to reduce subsequent settlement under working loads.
• Compaction increases the shear strength of the soil.
• Compaction reduces the voids ratio making it more difficult for water to flow through soil. This is important if the soil is being used to retain water such as would be required for an earth dam.
• Compaction can prevent the build up of large water pressures that cause soil to liquefy during earthquakes.
2 . Factors affecting Compaction
• Water content of the soil
• The type of soil being compacted
• The amount of compactive energy used
3. Field specifications :
To control the soil properties of earth constructions (e.g. dams, roads)
it is usual to specify that the soil must be compacted to some pre-determined dry unit weight.
This specification is usually that a certain percentage of the maximum dry density, as found from a laboratory test (Standard or Modified) must be achieved.
For example we could specify that field densities must be greater than 98% of the maximum dry unit weight as determined from the Standard Compaction Test.
It is then up to the Contractor to select machinery, the thickness of each lift (layer of soil added) and to control moisture contents in order to achieve the specified amount of compaction.
There are two principal types of compaction force :
1. Static Force:
It is simply the dead weight of the equipment. This is done by applying the downward force on the soil surface and compressing the soil particles. Static force is confined to upper soil layers and limited to the appreciable depth. Kneading and Pressure are two basic mechanisms of static compaction.
2. Vibratory Force:
It is usually an engine drive to create the downward force in addition to the weight of the machine. The vibrating mechanism is usually a rotating eccentric weight of the machine or piston combination. The compactors deliver a rapid sequence of blows to the surfaces, thereby affecting the top layers as well as deeper layers. Vibrations move the material, setting particles in motions and moves them close together for highest density possible.
The different types of compaction equipment used in compaction project depend on the scope of work. The compaction equipment to be used can either be used for some situations or can be a special type which meets the requirements of the particular project.
- a.Smooth Wheeled Roller
- b.Sheepsfoot Roller
- c.Pneumatic Roller
- d.Vibratory Roller
- e.Rammer
- f. Vibratory Plate Compactor.
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