Practical 2 Soil Compaction

Proctor compaction test
Theory
Compaction is the process of densification of soil by reducing air voids. The degree of compaction of a
given soil is measured in terms of its dry density. The dry density is maximum at the optimum water
content. A curve is drawn between the water content and the dry density to obtain the maximum dry
density and the optimum water content.
Dry density of soil:

Where M = total mass of the soil, V= volume of soil, w= water content.
Materials
Special
1. Standard proctor device
2. Mould 11.5cm high 10cm diameter (900cc)
3. Removable collar 6.25cm high 10cm diameter
4. Hammer 5cm diameter (2.2kg)
General
1. Moisture
2. No. 4 sieve (4.6mm)
3. Scoop
4. Straightedge and knife
5. Large mixing pin
6. Technical balance
7. Drying oven
8. Desecrator
9. Drying cans
Methodology
1. The empty mould is weighed (with the base but without the collar)
2. A 3kg representative specimen was obtained of the 6 soil samples which are to be tested.
3. Al soil lumps in a motor were broken with rubber-covered pestle and the soil was sieved through
a No.4 sieve (4.6mm)
4. The soil was passed from 5-8cm layer in the mould
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5. The soil was gently pressed to smooth its surface, and then it was compacted with 25 evenly
distributed blows of hammer using a 30cm free drop. The hammer was rotated slightly to ensure
the uniform distribution of blows.
6. The procedure was repeated with second and third layer.

7. The collar and trim were removed off the soil even with the top of mould. When removing the
collar, it was rotated to break the bond between it and soil before lifting it off the mould.
8. The trimming was done by using straight edge, beginning at the central axis towards the edge of
mould.
9. After the soil has been made even with the top of the mould and all the loose soil was cleaned
from outside and the soil was weighed to 4g.
10. The soil was removed from the cylinder using a jack and representative sample was obtained of
approximately 100g for water content determination. The water content sample was made up with
specimens from eh top, middle and bottom of the compacted soil.
11. The soil removed from the cylinder was broken up by hand, was remixed with the original sample
and its water content was arisen approximately 3% by adding water to the sample with the sprayer.
12. The water was distributed evenly and was mixed thoroughly. The weight of the water added was
obtained by measuring the weight of the sprayer before and after the spray.
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13. The compaction process was kept repeating until 5 or 6 runs have been made and the soil becomes
very wet and sticky.
Reading
Date: 2016-06-02
Location: Construction site of Sabaragamuwa University of Sri Lanka.
Mass of Mould: 5895 g
Volume of the Mould: 915.35 cm3
Container No
Weight of wet soil Weight of dry soil Weight of empty

+ container (g)
+ container (g)
container (g)
1-upper
1-middle
1-bottom
350
350
350
330
330
330
125
125
125
2-upper
2-middle
2-bottom
58.04
56.01
105.04
53.38
51.61
97.88
22.71
22.71
51.81
3-upper
3-middle
3-bottom
80.78
75.03
76.58
71.87
65.69
68.09
22.28
21.95
22.22
4-upper
4-middle
4-bottom
75.43
70.27
72.04
64.82
58.66
60.31
22.36
22.07
21.92
5-upper
5-middle
5-bottom
210
230
225
173.37
187.56
185.45
55
50
50
Calculation
Trial No
Mass of wet soil + mould (g)
Mass of the wet soil (g)
Wet density (g/cm3 )
I
9485
3590
1.703
Container NO
Average Mass of wet soil + Container (g)
Average Mass of dry soil + Cantainer (g)
Average Mass of Container (g)
Mass of dry soil (g)
Moisture content (%)
Dry density(g/cm3 )
II
10215
4320
2.05
I
350
330
125
205
9.76
1.552
3
III
10130
4235
2.018
II
73.03
67.33
32.41
34.92
15.32
1.778
IV
9955
4060
1.926
III
77.46
68.55
22.15
46.40
19.27
1.672
V
9755
3860
1.831
IV
72.58
61.26
22.11
39.15
29.08
1.492
V
221.66
182.12
51.66
130.46
30.7
1.401
Result
2
Max DD
1.8
0.1532, 1.778
Dry density(gcm3)
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0.05
0.1
0.15
OMC
0.2
0.25
0.3
0.35
Moisture content(%)
Conclusion
Compaction is the process by which the bulk density of an aggregate of matter is increased by driving
out air. For any soil, for a given amount of comp active effort, the density obtained depends on the
moisture content. At very high moisture contents, the maximum dry density is achieved when the soil is
compacted to nearly saturation, where (almost) all the air is driven out. At low moisture contents, the soil
particles interfere with each other; addition of some moisture will allow greater bulk densities, with a
peak density where this effect begins lo he counteracted by the saturation of the soil.
Discussion
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
comp active 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 comp active 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
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moisture content is then plotted to establish the compaction curve. The maximum dry density is finally
obtained from the peak point of lite compaction curve and its corresponding moisture content, also known
as the optimal moisture content.
Errors
1. Aggregations of dried soil not completely broken.
2. Water not thoroughly absorbed into dried soil.
3. Soil reused.
4. Insufficient number of range of water contents to define compaction curve accurately.
5. Improper foundation for compaction mould.
6. Mechanical compactor not properly calibrated.
7. Human factors in the operation of hand rammer.
References
1. http://theconstructor.org/geotechnical/compaction-test-soil-proctors-test/3152/
2. https://en.wikipedia.org/wiki/Proctor_compaction_test
3. Evaluation of Laboratory Compaction Techniques for Simulating Field Soil Compaction by W.
V. Ping, P.E., Guiyan Xing, Michael Leonard and Zenghai Yang (March 2003). Research Report
No.: FL/DOT/RMC/BB-890(F)

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Proctor compaction test

Dry density of soil:

6. The procedure was repeated with second and third layer.

Weight of wet soil Weight of dry soil Weight of empty

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