Introduction: The civil Engineering structures like the dams, pavements & canal banks etc are compacted to the maximum dry density to improve its strength properties. If the soil is compacted to a smaller volume it will have high shear strength, lower void ratio and lower permeability. If you take the earthen dams, then the required limit of the permeability of the dam is 0, which can be only achieved by the proper compaction by using some mechanical means. The dynamic loads are applied on the soil layer by layer and it is compacted to smaller thicknesses.
Why to study the compaction?:
(1)It is important to study the compaction techniques used to compact the soil used in the earthen structures like dams, pavements and the canal banks.
(2) It improves the strength characteristics of the soil, like its shear strength.
(3) It decreases the void ratio of the soil, so it makes it more dense.
(4) The permeability of the soil gets decreased to certain degree.
Concept of Compaction:
As we know that as of 2013 the soil mechanics is a newer science as compared to the other civil engineering sciences. R.R.Proctor proctor in 1933 gave a new concept to achieve the maximum dry density using a new compaction theory. He proposed that if we use the moisture in the soil while compaction, we can achieve the higher dry densities. He experimented with the addition of the moisture to the soil to be compacted, and he plotted a curve between the added moisture content of the soil and the achieved dry density under the same compaction effort. The curve showed that the dry density of the soil increases with the addition of the moisture while compaction, and it achieves a maximum limit and if we further increase the moisture content then the dry density starts to decrease.
The moisture content at which the soil can be compacted to the maximum dry density is known as the optimum moisture content(O.M.C.). So after getting the experiment done on various fine soils, he got the similar curves and different values of the O.M.C. for the different soils.
So he defined the optimum moisture content(O.M.C.) as the water content at which the soil achieve its maximum dry density using the compaction techniques.
For calculating the dry density of the soil in the field test you can use the following formula
Dry Density = Bulk Density/ (1+ water content)
Field Control of Compaction:
Field control of compaction is done to achieve the 90 to 95% of the maximum dry density achieved in the laboratory tests. Field control of the compaction is done by:
(1) Regularly checking the achieved dry density of the soil.
(2) Moisture content of the soil.
For regular checking of the dry density of the soil you can use the above mentioned formula, i.e.
Dry Density = Bulk Density/ (1+ water content)
Bulk density can be easily find out using the methods like sand replacement method and the water content can also be found out easily by the proctor needle method if the oven method is time consuming.
The moisture content at which the soil can be compacted to the maximum dry density is known as the optimum moisture content(O.M.C.). So after getting the experiment done on various fine soils, he got the similar curves and different values of the O.M.C. for the different soils.
So he defined the optimum moisture content(O.M.C.) as the water content at which the soil achieve its maximum dry density using the compaction techniques.
For calculating the dry density of the soil in the field test you can use the following formula
Dry Density = Bulk Density/ (1+ water content)
Field Control of Compaction:
Field control of compaction is done to achieve the 90 to 95% of the maximum dry density achieved in the laboratory tests. Field control of the compaction is done by:
(1) Regularly checking the achieved dry density of the soil.
(2) Moisture content of the soil.
For regular checking of the dry density of the soil you can use the above mentioned formula, i.e.
Dry Density = Bulk Density/ (1+ water content)
Bulk density can be easily find out using the methods like sand replacement method and the water content can also be found out easily by the proctor needle method if the oven method is time consuming.
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