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NO. PARTICAL WORK : 4 (CHAPTER 3)

TITLE OF PARTICAL WORK : THE STANDARD PROCTOR COMPACTION

TEST

OBJECTIVE : To determine soil density in laboratories

THEORY :

A compaction test is a soil quality test used to assess the level of compaction which can

occur in the soil on a site. Compaction tests are commonly performed as part of a geotechnical

profile of a building site. They may also be performed to learn more about a soil in a particular

area, whether or not the area is slated for development. A geotechnical engineer, geologist, or soil

scientist may conduct a compaction test.

In some cases, the test may be performed in situ, in which case the testing options may be

more limited, and the profile will not be as complete. Compaction tests can also be performed in a

lab environment with soil samples taken from a site. The lab allows for more controls and more

finesse of the test. Soil often needs to be taken back to the lab anyway for the performance of

additional soil quality tests which are designed to provide more information about the

characteristics and composition of the soil.

The Proctor compaction test is a laboratory method of experimentally determining the

optimal moisture content at which a given soil type will become most dense and achieve its

maximum dry density. The term Proctor is in honor of R. R. Proctor, who in 1933 showed that the

dry density of a soil for a given compactive effort depends on the amount of water the soil contains

during soil compaction. His original test is most commonly referred to as the standard Proctor

compaction test; later on, his test was updated to create the modified Proctor compaction test.

These laboratory tests generally consist of compacting soil at known moisture content into

a cylindrical mould of standard dimensions using a compactive effort of controlled magnitude. The

soil is usually compacted into the mould to a certain amount of equal layers, each receiving a

number blows from a standard weighted hammer at a specified height. This process is then

repeated for various moisture contents and the dry densities are determined for each. The graphical

relationship of the dry density to moisture content is then plotted to establish the compaction

curve. The maximum dry density is finally obtained from the peak point of the compaction curve

and its corresponding moisture content, also known as the optimal moisture content.

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Figure 1 : Compaction Mold

EQUIPMENT :

The equipment for determination of density for standard proctor compaction test includes:

i. Compaction Mold

ii. Standard Proctor rammer – 2.5kg

iii. Sieve no #4 ( size 4.75mm )

iv. Ruler

v. Moisture Can

vi. Electronic Balance

vii. Large flat pan

viii. Drying oven

ix. Measuring Cylinder

x. Soil 3.0 kg

PROCEDURE :

1. About 5.0 kg air-dry soil samples are prepared to be sieved on a No. 4 sieve. All the lumps

are broken down to avoid reducing the size of particles.

2. The combined weight of the proctor mold + the base plate + extension top of the mold, W1

(kg) is determined.

3. 3% water is added to the soil. Divide the soil into three layers. Each layer was compacted

uniformly with 27 blows from Standard Proctor rammer weighing 2.5kg.

4. The third layer was slightly compacted above the top of the rim of the compaction mold.

5. The combined weight of mold + base plate + extension top of the mold + compacted soil,

W2 (kg) is determined.

6. The base plate from the mould is removed.

7. The compacted soil cylinder was extruded from the mold using a jack.

8. The weight of empty moisture can, C1 is determined.

9. Moist soil was obtained from the compacted soil cylinder and the combined weight of the

moisture soil, C2 is determined.

10. The moisture can with moist soil was placed in the oven to dry to a constant weight.

11. The remaining compacted soil is returned to the mixing bowl.

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12. Through the use of the mixing spoon and our hands, the compacted soil cylinder is broken

down and remixed with the left over moist soil.

13. More water was added and it was mixed to raise the moisture content by 2%.

14. Steps 3 – 12 were repeated. In this process, the value of W2 will first increase with

increasing moisture content, but will then decrease. The test was continued until at least

two successive down readings were obtained.

15. Upon our return to the lab the following day (24hrs after placing the can), the combined

mass of Moisture cans + dry soil samples, C3 was determined.

REPORTING OF RESULTS:

Form 4.A of the BS 1377-4:1990 is used. Refer to attachment.

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CONCLUSION :

REFERENCE (S) :

1. BS1377-4:1990 (Part 4), Form 4.A – Page 45

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ATTACHMENTS :

(Related Figures from BS 1377-4:1990)

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