Free Report On Compaction Tests

Introduction

Compaction of soils relates to the process of packing soil particle more closely through using mechanical means such as rollers. The purpose is to increase the dry density of the soil. Soil compaction is normally achieved through a reduction of air voids present in the soil, with little or no reduction in moisture content. In the presence of low moisture levels, thin films of water surround soil particles. Increasing the moisture content levels lubricates the soils particle making them easier to compact (lubrication). Compaction of soil will continue to increase up to an optimum water content. At this limit, excess water begins to push soil particles apart. At these high levels of moisture content, air is less or is completely removed, and the addition of more water reduces the dry density.

Standard Proctor Test

Purpose: The standard compaction test was carried to establish the compaction characteristics of the soil sample.
Equipment
Compaction mold
No. 4 sieve
Standard Proctor hammer (5.5 lb (24.5N)

Balance, sensitive up to 0.01 lb

Balance, sensitive up to 0.1g
Large flat pan
Jack
Steel straight edge
Moisture cans
Drying oven
Plastic squeeze bottle with water
Procedure
About 10lb of air-dry soil was obtained and the soil lumps broken.
The soil was then sieved through a sieve No. 4. The minus-4 material collected in the large pan was about 6 lb.
Water was then added to the large pan containing the soil to increase the moisture content to about 5% and mixed thoroughly.

The weight or mass of the Proctor mold and the base plate was then determined (W1)

The extension or collar was then attached, and the moist soil poured in three equal layers. Each layer was compacted using the standard proctor hammer 25 times before adding another layer of loose soil.
Once the three layers were compacted, the collar was removed while ensuring that compacted soil inside the mold did not break off.
A straight edge was then used to trim the excess soil above the mold to make the soil even with the top surface of the mold.

The eight of the mold plus the base plate and the compacted soil was measured (W2)

The base plate was removed, and a jack was used to extrude the compacted soil from the cylinder.
A sample of the extruded soil was then put in a can, measured, and then oven dried.
The remaining compacted soil was crushed by hand and mixed with the remaining soil in the pan. Water was then added to raise the moisture content by 2%.
The steps from 6 to 11 were then repeated until the weight of the mold plus the base plate and compacted soil reduced (At least two successive readings).

Modified Proctor test

Purpose: the modified proctor test is used to determine the compaction characteristics of soils especially where higher densities are necessary such as in the construction of dams.
Equipment
Compaction mold
No. 4 sieve
Standard Proctor hammer (5.5 lb (24.5N)
Balance, sensitive up to 0.01 lb
Balance, sensitive up to 0.1g
Large flat pan
Jack
Steel straight edge
Moisture cans
Drying oven
Plastic squeeze bottle with water
Procedure

About 10 lb of air-dry soil sample was obtained and the soil lumps broken.

The soil was then sieved through a sieve No. 4. The minus-4 material collected in the large pan was about 6 lb.
Water was then added to the large pan containing the soil to increase the moisture content to about 5% and mixed thoroughly.
The weight or mass of the Proctor mold and the base plate was then determined (W1)
The extension or collar was then attached, and the moist soil poured in five equal layers. Each layer was compacted using the standard proctor hammer 25 times before adding another layer of loose soil.
Once the five layers were compacted, the collar was removed while ensuring that compacted soil inside the mold did not break off.
A straight edge was then used to trim the excess soil above the mold to make the soil even with the top surface of the mold.

The weight of the mold plus the base plate and the compacted soil was measured (W2)

The base plate was removed, and a jack was used to extrude the compacted soil from the cylinder.
A sample of the extruded soil was then put in a can, measured, and then oven dried.
The remaining compacted soil was crushed by hand and mixed with the remaining soil in the pan. Water was then added to raise the moisture content by 2%.
The steps from 6 to 11 were then repeated until the weight of the mold plus the base plate and compacted soil reduced (At least two successive readings).

Test results

Standard Proctor Test

Moisture Content Determination

Modified Proctor test
Moisture content determination
The maximum dry density is 144.4 lb/ft3
The optimum moisture content is 1.48%
Discussion
The standard Proctor test is used in most cases to determine the compaction characteristics of soils in cases where heavy compaction levels are not required (Das and Sobhan 147). The Modified Proctor test is used in cases where higher densities of compaction are required (Ramamurthy and Sitharam 168). For instance, in cases such as road construction and dam construction, higher densities are required.
According to Ranjan (109), water acts as a lubricant to the soil particles at low moisture contents. At the low moisture contents, the soil particles have a higher resistance to compaction. As the water is increased, the soil particles become easier to work on thus are compacted easily causing an increase in the dry density until optimum moisture content is reached. A further increase in water content causes the water to replace the soil particles hence the dry density decreases. This is evidently observed in Test 3 (dry density of 160.077 lb/ft3) and Test 4 (158.051 lb.ft3) for the modified Proctor test.
Soil compaction is performed to increase the strength characteristics of soils and to increase the bearing capacity of the foundation constructed over them (Das and Sobhan 146). Additionally, compaction reduces undesirable settlement of structures and increases the stability of slopes of embankments (Das and Sobhan 146). Knowledge of the optimum moisture content is significant. It allows soils to be compacted to a maximum grade with the least amount of effort and permit the compacted soil to attain the lowest level of permeability.
Errors were observed in the standard Proctor test. Details collected for water content for Test 1 Can No. 3 indicated an increase in the weight of the can plus the dry soil after oven drying. As such, it is probable that errors were made during measuring of the weight of the moist soil plus the can.

Conclusion

The experiment was partly a success owing to the results obtained from the modified proctor test. However, the standard Proctor test data values for moisture content were inaccurate because of the errors made in collecting the readings for moisture content. The maximum dry density from the modified proctor test was 144.04 lb/ft3, and the optimum moisture content was 1.48%.

Works Cited

Das, Braja, and Khaled Sobhan. Principles of Geotechnical Engineering. Stamford: Cengage Learning, 2013. Print
Ramamurthy, T, and T G. Sitharam. Geotechnical Engineering: Soil Mechanics. New Delhi: S. Chand, 2010. Print.
Ranjan, Gopal. Basic and Applied Soil Mechanics. Print.
Appendix
Sample Hand Calculations