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PROCTOR COMPACTION

TEST

SOIL MECHANICS

SOIL MECHANICS LABORATORY DEPARTMENT OF CIVIL ENGINEERING UNIVERSITY OF MORATUWA

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Standard Proctor Compaction Test

General

The purpose of the standard Proctor compaction test is to determine the optimum water content and the maximum dry density that can be achieved with a certain compaction effort. The relationship between the moisture content and the density of the soil will be obtained in the process. Compaction effort designed in this laboratory test is comparable with that obtained in the field. Compaction is the process of increasing the bulk density of the soil or aggregate by driving out the air. For a given soil, for a given amount of compaction effort, the density obtained depends on the moisture content.

Scope

The method given in this standard is based on the standard proctor compaction test. Soil is compacted in a mould in three layers by dropping a 2.49 kg rammer a distance of 305mm. (Alternatively dropping a 2.5 kg ramrner 300 mm). Dry density achieved by mixing soil with different water contents were determined to obtain the maximum dry density and the corresponding optimum moisture content.

There are four alternative procedures as listed below;

• A - With a 101.6 mm diameter mould for material passing 4.7.5 mm sieve,

• B - With a 152.4 mm diameter mould for material passing 4.7.5 mm sieve,

• C - With a 1-52.4 mm diameter mould for material passing 19.0 mm sieve,

• D- With a 1·52.4 mm diameter mould for material passing 19.0 mm Sieve, Corrected by replacement for material retained on a 19.0 mm sieve,

Methods A and B

With methods A and/or B no oversize correction is required unless the material retained in 4.75 mm sieve is greater than 7%. In that case material retain in 4.75 mm sieve may be discarded. When material retained on 4.75 mm sieve is greater than 7%, method C should be used.

Method C

With method C unless the material retained in 19.0 mm sieve is greater than 10%, no oversize correction should be used. If the amount of material retained on 19.0 mm sieve is greater than 10%, method D should be used.

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Method D

Material retained on 19.0 mm sieve should be passed through 75 mm sieve. Material retained on 75 mm sieve shall be discarded. Material passing the 75 mm sieve and retained on the 19 mm sieve shall he replaced with all equal amount of material passing a 19 mm sieve and retained 4.75 mm sieve. Material for replacement shall be taken from the unused portion of the sample.

Apparatus

The following apparatus are required,

a) Moulds - There shall be cylindrical moulds conforming to the moulds described above. The

mould of diameter 101.6 mm shall have a height of 116.4 mm, and therefore will be of a volume 944 cm3.

The mould of 152.4 mm shall have a height of 116.4 mm, and therefore will be of a volume 2124 cm3.

The moulds shall be fitted with a detachable base plate and a removable extension approximately 50 mm high.

b) A metal Rammer - There shall be a metal rammer having a 50 mm diameter circular face, and weighing 2.49 kg. The rammer shall be equipped with a suitable arrangement for controlling the height of drop to 305mm. ( Alternatively there can be rammer of 2.5 kg weight with a drop 300 mm)

c) Balances - A balance readable and accurate to 1 g ( with a capacity 20 kg) and a balance readable and accurate to 0.01 g,

d) Sieves - A 75 mm sieve, a 19 mm sieve and a 4.75 mm sieve.

e) Mixing tools - Miscellaneous tools such as mixing pan, spoon, trowel, spatula etc.

f) Metal tray - A large metal tray ( 600 mm X 500 mm and 80 mm deep),

g) Straightedge - A Steel straightedge, 300 mm long, 25 mm wide, and 3 mm thick with one

beveled edge,

h) Sample extruder - (Optional) An apparatus ( such as a jack) for extruding specimen from

the mould,

i) An oven - Thermostatically controlled oven to provide temperature 105 -110 Co,

j) Cans - Cans to take samples for moisture content determination,

ρ = M2 – M1 V w= M4 – M5 M4 – M3

ρ

d = ρ (1 + w)

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Procedure

1. Obtain approximately 3 kg of air – dried soil in the mixing pan, break all the lumps so that it passes the sieve given in method A, B, C and D

2. Add suitable amount of water (See Note 1)

3. Determine the weight of the empty mould without the base plate and the collar (M1) to the

nearest 1g

4. Fix the collar and the base plate

5. Compact the moist soil in to the mould in three layers of approximately equal mass

(Each layer shall be compacted by 25 blows in the case of 101.6 mm diameter mould and 56 blows in the case of 152.4 mm diameter mould. Blows must be distributed uniformly over the surface of each layer so that the rammer always falls freely. The amount of soil must be sufficient to fill the mould, leaving not more than 6mm to be struck off when the extension is removed. (Note 03))

6. Detach the collar carefully without disturbing the compacted soil inside the mould and using a straight edge trim the excess soil leaving to the mould

7. Obtain the weight of mould with the moist soil (M2) after removing the base plate

8. Extrude the sample and break it to collect the sample for water content determination preferably at least two specimens one near the top and other near the bottom

9. Weigh an empty moisture can, M3 and weigh again with the moist soil obtained from the

extruded sample in step 8 (M4)

10. Keep this can in the oven for water content determination

11.Repeat step 4 to 10. During this process weight M2 increases for some time with the increase

in moisture and decreases thereafter. Conduct at least two trials after the weight starts to reduce. ρ = M2 – M1 V w= M4 – M5 M4 – M3

ρ

d = ρ (1 + w)

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12.After 24 hours get the weight of oven dried sample (M5)

Computations

The bulk density, ρ in kg/m3 of each

compacted specimen shall be computed from the equation;

Moisture content can be obtained from the equation;

Where w is the moisture content of the soil as a fraction.

The dry densities

ρ

d, obtained in a series of determinations shall be plotted against the

corresponding moisture content, w. A smooth curve shall be drawn through the resulting points and the position of the maximum on this curve shall be determined. Thus the maximum dry density and

Where;

M1 is the mass of the mould and base, in kg

M2 is the mass of mould, base and soil, in kg

V is the volume of the mould in m3

ρ = M2 – M1 V w= M4 – M5 M4 – M3

ρ

d = ρ (1 + w)

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the corresponding water content should be obtained from the graph.

Presentation of Results

The maximum dry density shall be reported to the nearest kg /m3, and the optimum moisture content

shall be reported to the nearest 0.01 %.

Note 1

-The amount of water to be added with air dried soil at the commencement of the test will vary with the type of soil under test. In general, with sandy and gravely soil a moisture content of 4% to 6% would be suitable, while with cohesive soils a moisture content of about 8% to 10% below the plastic limit of the soil, would be usually be suitable.

Note 2

-It is important that the water is mixed thoroughly and adequately with the soil, since inadequate mixing gives rise to variable test results. This is particularly important with cohesive soil when adding a substantial quantity of water to the air dried soil.

With clays of high plasticity, or where hand mixing is employed, it may be difficult to distribute the

water uniformly through the air dried soil by mixing alone, and it may be necessary to store the mixed sample in a sealed container for a minimum period of about 16 hours before continuing with the test.

Note 3 -

It is necessary to control the total volume of the soil compacted; since it has been found that if the amount of soil struck off after removing the extension is too great, the test results will be inaccurate.  Note 4 -

The water added for each stage of the test should be such that a range of moisture contents is obtained which includes the optimum moisture content. In general, increments of 1 % to 2% are suitable for sandy and gravely soils and of 2% to 4% for cohesive soils. To increase the accuracy of the test it is often advisable to reduce the increments of water in the region of the optimum moisture content.

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Proctor Compaction Test – Specimen work sheet

University Of Moratuwa

Soil Mechanics Laboratory Proctor Compaction Test Results

Moisture Content Sample 1 Moisture Content sample 2 Average m. c. and Dry Density Trial Mass of Mass of

Mould + Soil (kg) Moisture can No Mass of wet soil+can (g) Mass of dry soil+can (g) Mass of can (g) m. c 1 Moisture can No Mass of wet soil+can(g) Mass of dry soil+can(g ) Mass of can (g) m. c 2 Ave. mc % Bulk Density Kg/m3 Dry Density Kg/m3 No. Mould kg 1 1.954 3.752 9 129.840 124.93 9.83 0.0427 k5 151.41 145.47 9.17 0.0436 4.31 1904.66 1825.93 2 1.954 3.813 12 145.830 138.26 10.26 0.0591 er 164.72 156.46 27.42 0.0640 6.16 1969.28 1855.05 4 1.954 3.915 f 134.170 124.88 10.13 0.0810 f56 188.62 175.41 28.78 0.0901 8.55 2077.33 1913.66 5 1.954 4.018 g1 123.590 112.93 10.60 0.1042 h7 120.59 109.69 8.79 0.1080 10.61 2186.44 1976.71 6 1.954 4.036 g6 134.500 120.76 10.13 0.1242 h89 126.35 112.96 10.26 0.1304 12.73 2205.51 1956.47 7 1.954 4.033 78 123.590 110.38 8.21 0.1293 ki 125.15 111.22 9.55 0.1370 13.32 2202.33 1943.54 8 1.954 3.976 k 139.200 121.32 8.74 0.1588 kp 112.97 97.56 8.45 0.1729 16.59 2141.95 1837.20

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Specimen Calculation

Consider set 2 (Trial number 2)

M ass of compacted soil inside the mould = 3.813 - 1.954 = 1.859 kg Volume of the mould = 944 cm 3

Bulk density of the soil = 1.859/( 944 x 10-6)

= 1969.28 kg/m3

M oisture content Sample 1

M oisture content = M ass of water/mass of dry soil = (145.83-138.26)/(138.26-10.26) = 0.0591

M oisture con lent Sample 2

M oisture content = M ass of water/ mass of dry soil = (164.72-156.46)/(156.46 - 27.42) =0.0640

Average moisture content = (0.0591+0.0640)/2.0 = 0.0616 = 6.16 % Dry Density = 1969.28/(1 +0.0616)

= 1855.05 kg / m3

Plot dry density against the moisture content

The peak will give the maximum dry density achieved

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Maximum Dry Density = 1978 kg/m3

References

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