The following article will guide you about how to conduct IS compaction test for soil.
Equipment used for the IS Compaction Test:
The equipment for the test, as shown in Fig.12.2, consists of the following:
1. Compaction Mold:
It is a cylindrical mold of 10 cm internal diameter and 12.73 cm internal height with a total volume of 1000 cm3. It is made of copper alloy or brass and is attached to a mild steel base plate.
The rammer consists of a 2.6 kgf weight, falling through a height of 31 cm to apply blows on the soil for compaction. It is made of mild steel or brass and the base has a diameter of 5 cm.
About 6 kgf of soil passing 20-mm IS sieve is taken for the test. When sieved through 20-mm IS sieve, the soil retained on IS sieve should not be more than 5% for accurate results. If more than 5% of soil is retained on 20-mm IS sieve, it will lead to errors in the result. In such cases, the soil passing 40-mm IS sieve should be used for the test. In this case, a bigger compaction mold of 15 cm internal diameter and 12.73 cm internal height with a total volume of 2250 cm3 is used.
Procedures Adopted for Conducting IS Compaction Test:
1. Aggregations of soil particles are broken and the soil is mixed with a suitable amount of water. The amount of water to be added initially for the first trial is 4%–6% for sandy or gravelly soil and 8%–10% below plastic limit (PL-8 or PL-10) of the soil for cohesive soils.
2. The soil and water should be mixed thoroughly It is required to store mixed sample in a sealed container for about 16 h in the case of high plastic clays for the uniform distribution of moisture throughout the volume of the soil.
3. The compaction mold with the base plate attached is weighed to the nearest 1 g using a balance of capacity 10 kgf (W0).
4. The mold with base plate is placed on a solid base such as concrete floor. About 2.5 kgf of the wet soil is taken and divided approximately into three parts. One part of the wet soil is placed in the mold and compacted by applying 25 blows with the 2.6 kgf rammer, falling through exactly 31 cm on the soil for each blow. The blows should be uniformly distributed over the entire area of the mold.
5. The second and third parts of the soil are also placed in the compaction mold successively, each time compacting this soil with 25 blows. Before placing the third part of soil into the mold, the collar is attached to the top of the mold to accommodate the entire loose soil and for applying the blows effectively.
6. The collar is now removed from the top of the mold and excess soil above the top of the mold should be trimmed off and the surface is leveled with a straight edge. The amount of soil placed in the mold should be just sufficient so that the compacted soil does not project more than 5 mm above top of the mold.
7. The mold with the base plate along with the compacted soil is then weighed to the nearest 1 g (W1).
8. The compacted soil is now removed from the mold and placed in the tray. A representative sample of soil is taken for water content determination (ω1).
9. The remainder of the compacted soil specimen is broken up to individual particle level by hand knife and by rubbing through the 20-mm IS sieve, and then mixed with the remainder of the original sample.
10. The inside surface of the compaction mold collar and rammer are cleaned of soil.
11. Suitable amount of water is now added to the wet soil, 1%-2% for sandy or gravelly soils and 2%-4% for cohesive soil.
12. The procedure in steps 2-11 is repeated to get a total of at least five trials, so that the weights W1, W2, W3, W4, and W5 and the corresponding water contents ω1, ω2, ω3, ω4, and ω5 are obtained. The range of water content covered with the trails should be such that the OMC lies between ω2 and ω4.
1. The bulk density and dry density are computed for each trial using Eqs. (12.1) and (12.2), respectively, as follows:
γ1 = (W1 – W0)/V …(12.1)
γd1 = γ1/(1 + ω1) …(12.2)
where for Eq. (12.1) γ1 is the bulk density in the first trial, W1 the weight of the mold + base plate + compacted, W0 the weight of empty mold + base plate, and V the volume of the mold and for Eq. (12.2) γd1 is the dry density in the first trial and ω1 the water content in the first trial.
2. The values of γd2 to γd5 for water contents W2 to W5 are similarly computed using Eq. (12.2).
3. A graph is plotted with the water content on the x-axis and the dry density on the y-axis. The experimental points are joined by a smooth curve, which is known as the compaction curve.
4. The Maximum Dry Density (MDD) is read from the compaction curve and the water content corresponding to MDD is taken as OMC.
Precautions to be Taken while Conducting IS Compaction Test:
1. In case more than 5% of soil is retained on 20-mm IS sieve, the soil passing 40-mm IS sieve should be used. In this case, the bigger mold of 15 cm diameter, 12.73-cm height with 2250 cm internal volume is used. The soil is compacted in three layers using 55 blows of the 2.6 kgf rammer for each layer.
2. For soils that are susceptible to crushing, each trial of determining W and ω should be done using a fresh soil sample instead of using the compacted soil. In this case, the water added for each trial should be the sum of water added in the preceding trial and the increment of water.
The soil is considered susceptible to crushing if the sample contains granular material of a soft nature such as soft lime stone, sand stone, and others, which is reduced in size by the action of the 2.6 kgf rammer.
3. The inside surface of the mold and collar and also the inside surface of the rammer tube should be kept clean before each trial or silicon grease may be smeared to the surface of the mold to facilitate removal of compacted soil at the end of each trail.
4. The success of the experiment depends on thorough mixing of soil and water. Sufficient time should be allowed, after mixing soil and water, for permeation and distribution of moisture throughout the voids of the wet soil before compaction of soil in each trial.
Report Obtained from IS Compaction Test:
The MDD should be reported to the nearest 0.01 g. IS – 10074-1982 gives specification for compaction mold assembly. IS – 9198-1978 (reaffirmed 1987) gives specification for the rammer to be used for compaction test.