Objective:
Determine the maximum dry density at the optimum moisture content under
laboratory condition.
Theory:
The test consists of compacting the soil or aggregate to be tested into a
standard mould using a standardized compactive energy at several different
levels of moisture content. The maximum dry density and optimum moisture
content is determined from the results of the test.
Soil in place is tested for in-place dry bulk density, and the result is divided
by the maximum dry density to obtain a relative compaction for the soil in
place.
In the other hand, soil compaction test is carried out in the laboratory in
determining the ideal volume of water to be poured while compaction the
soil on site so that the required compaction degree can be obtained.
The important characteristics of soil compacted with an ideal compaction
degree are:
a ) H i g h sh ea r s t r en g t h
b) Low permeability coefficient and capacity
c)Reduce settlement when additional load is applied
The moisture content recorded when the maximum dry unit weight is
achieved is known as the optimum moisture content. There are two types
of compaction i.e.:
1.Standard protector
2.Modifier protector
Standard Proctor will be used in undertaking the experiment where the
standard data are recorded as the following:
Equipment’s:
1. Soil sample.-about 3kg
2. Moulds
3. A metal harmer
4. Balances
5. Balances
6. Sieves
7. Mixing tools- mixing plan, spoon, trowel, spatula and etc.
8. Metal try
9. straight edge
10. Sample extruder
11. An oven
12. Graduated jar
13. Water
Procedure:
1. Small soil sample from jobsite collected.
2. 3kg of dry soil passing through 4.75mm sieve opening prepared.
3. Empty mould, collar and base plate weighed. The empty containers also
weighed.
4. The sample mixed thoroughly with approximately 9% water of the total
soil volume.
5. The soil sample divided into three sections.
6. The any first section placed in the mould and compacted. Distribute
25blows uniformly over the surface and ensure that rammer always falls
freely and is not obstructed by soil in the guide tube.
7. The second section place into the mould and being compacted followed
by the last section of soil sample.
8. The attached collar removed when the compaction completes.
9. The compacted soil trimmed using the straightedge until it is even with
the top of the mould.
10. Small amount of soil from the upper mould taken and placed into a
container.
11. Then the container with the soil sample being weighed.
12. Small amount of soil from the bottom mould taken and placed into a
container.
13. Then the container with the soil sample being weighed.
14. Both containers placed into an oven to determine its moisture contain.
15. The compacted soil’s sample unit weight determined by dividing the
weight of the compacted soil in the mould with the soil sample volume
(volume of the mould).
Discussion:
Compaction is the process of mechanically densifying a soil. 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. Mechanical compaction is one of the most common and cost effective means of stabilizing soils.
Mechanical compaction implies dynamic compaction or densification by the application of moving loads to the soil mass. Soil compaction is one of the most critical components in the construction of roads, airfields, embankments, and foundations. The durability and stability of a structure are related to the achievement of proper soil compaction. Principal soil properties affected by compaction include:
Strength Resistance to shrinkage Settlement Shearing resistance Movement of water Volume change
Normal soils consist with a large portion of air pockets. That’s the reason why it’s capable to compact soil. While compaction air is taken out hence the density of soil is increased. But due to the various shapes of soil particles it is impossible to take out all the air inside. Therefore, we introduce moisture to the system. Moisture can go through the air pockets and fill the voids. And in the meanwhile it allows soil particles to move more flexibly. So a good compaction level can be achieved.
If we add moisture little by little and check the dry density, we can see a decreasing increment. On one occasion all the voids fill with moisture.
If we keep adding moisture after that also what happen is moisture try to displace soil particles. But soil particles are far denser than water particles. Therefore, with adding
excessive water amount we can see a gradual decrement of dry density. So at particular moisture content we can obtain the maximum dry density.
The optimum water content is the water content that results in the greatest density for a specified compactive effort.
Compacting at water contents higher than the optimum water content results in a relatively dispersed soil structure that is weaker, more ductile, less porous, softer, more susceptible to shrinking, and less susceptible to swelling than soil compacted dry of optimum to the same density. The soil compacted lower than the optimum water content typically results in a flocculated soil structure (random particle orientations) that has the opposite characteristics of the soil compacted wet of the optimum water content to the same density.
It is said that the compaction level achieved by the proctor test is somewhat similar to the compaction levels of construction sites under medium sized rollers.
