The Standard & Modified Proctor Density Tests

Revised 2003, WKS Datasheet No. 7
MOHAWK COLLEGE OF APPLIED ARTS AND TECHNOLOGY
BUILDING AND CONSTRUCTION SCIENCES DEPARTMENT
The Standard & Modified Proctor Density Tests
INTRODUCTION:
In placing fill, it is often necessary and desirable to compact the fill to assure that the soil has
sufficient shear strength, that it will not settle excessively or both. In the field various machines are
used to carry out the compaction such as sheepsfoot rollers, rubber-tired rollers, etc. These compact
the soil to varying degrees depending on the efficiency of the roller for the particular soil, the
number of passes, etc. The density of the soil can be measured in the field by some form of field
density test. The Standard Proctor Test provides one means of compacting the soil in the laboratory
to determine the optimum moisture content and the maximum density.
The Standard test will be carried out in the first laboratory session and the Modified test will be
carried out in the following session. The results will be combined and submitted as one report.
The A.S.T.M. standard permits four variations in the test procedure.
Method A: 4 inch (101.6 mm) mould (volume 1/30 ft 3 or 1/1060 m 3 ), soil passing a No. 4(4.75 mm)
sieve.
Method B: 6 inch (152.42 mm) mould (volume 1/13.3 ft 3 or 1/471 m 3 ), soil passing a No. 4(4.75
mm) sieve.
Method C: 4 inch (101.6 mm) mould, soil passing a ¾ inch (19.0 mm) sieve.
Method D: 6 inch (152.4 mm) mould, soil passing a ¾ inch (19.0 mm) sieve.
EQUIPMENT (Standard Test):
Method A will be used in the Standard test and method B in the Modified test. In addition to the
mould, the following equipment will be required for the Standard test:
a) 5.5 lb (2.49 kg) rammer with controlled 12 inch (305 mm) drop
b) balance sensitive to 1 g.
c) balance sensitive to 0.1 g
d) 12 inch steel straight edge
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e) mixing tools, pans, moisture containers, etc.
f) oven for drying moisture content samples.
PROCEDURE (Standard Test):
1. Either mix 4 kg of sand and 400 g of bentonite or if the soil is pre-mixed take about 4½ kg. Break
up any lumps in the sample and mix it thoroughly.
2. Add about 9.5% water to the sample or as given by the instructor and mix thoroughly until all the
water is uniformly absorbed.
3. Weigh the empty mould without the collar or base and record its mass.
4. With the collar attached to the mould, compact a specimen in three equal layers to get a total
compacted depth of about 130 mm with 25 uniformly distributed blows of the rammer per layer.
During compaction the mould should rest directly on the concrete floor of the lab and not in the
mixing pan.
5. Remove the collar from the mould and strike off the soil with the straight edge even with the top
of the mould. Weigh the mould and the soil and record their mass. Subtract the mass of the
mould from the specimen and multiply by 1060 and record the result as the wet density of the
compacted specimen in kg/m 3 .
6. Remove the soil from the mould using the arbour press. Obtain a moisture content sample of
about 120 g from the centre of the specimen, weigh and place in the oven to dry.
7. Break up the sample and remix with the material that was not used in the test and add
approximately 2% more water. Remix and repeat the compaction procedure and obtain the
moisture content of the sample. This procedure is repeated again and again until two successive
decreases in the wet density of the compacted soil are observed. A minimum of 5 points are
normally required to plot the moisture density curve.
CALCULATIONS (Standard Test):
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Wet density: (The volume of the 4" mould is m )
1060
where
ρ = M x 1060
ρ = wet density in kg/m 3
M = mass of wet soil contained in the mould in kg (does not include the mould)
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Moisture content:
M w
w =
M s
where
w = moisture content in percent
Mw = mass of water in the moisture sample
Ms = mass of the dry moisture sample
Dry Unit Weight:
where
ρ
ρ d =
1
Zero Air Voids:
( + w)
ρd = the dry density of the soil
ρ = the wet density of the soil
w = the moisture content of the soil
G
=
1+
wGs
x ρ
s
ρ d
w
ZAV
where Gs = the specific gravity of the compacted soil (Assume Gs = 2.750)
ρw = the density of water (1000 kg/m 3 )
w = the moisture content of the soil
EQUIPMENT (Modified Test):
6 inch (152.4 mm) mould,
10 lb (4.54 kg) rammer with controlled 18 inch (457 mm) drop
balance sensitive to 1 g
balance sensitive to 0.1 g
12 inch steel straight edge
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mixing tools
oven for drying moisture content samples.
PROCEDURE (Modified Test):
1. Take 6 000 g of sand and mix with 600 g of bentonite or if pre-mixed soil is available about 6½
kg.
2. Add about 7% water to the sample or as given by the instructor and mix thoroughly until all the
water is uniformly absorbed.
3. Weigh the empty mould without the collar or base and record its mass.
4. With the collar attached to the mould, compact a specimen in five equal layers to get a total
compacted depth of about 130 mm with 55 uniformly distributed blows of the rammer per layer
of the specimen. During compaction the mould should rest directly on the concrete floor of the
lab.
5. Remove the collar from the mould and strike off the soil with the straight edge. Weigh the mould
and soil and record their mass. Subtract the mass of the mould from the specimen and multiply
this mass by 471 and record the result as the wet density in kg per cubic metre of the compacted
specimen.
6. Remove the soil from the mould. Obtain a moisture content sample from the centre of the
specimen, weigh and place in the oven to dry. The moisture content sample should weigh
approximately 100 g.
7. Break up the sample and re-mix with the material that was not used in the test and add
approximately to 2% more water. Re-mix again and repeat the compaction procedure and obtain
the moisture content of the sample. This procedure is repeated again and again until, for two
trials, there is a decrease in the wet density of the compacted soil. A minimum of 5 points will be
required to plot the moisture density curve.
CALCULATIONS (Modified Test):
1 3
Wet density The volume of the 6 inch mould is or (0.002124) m
471
where
ρ = M x 471
ρ = wet density in kg/m 3
M = mass of wet soil contained in the mould in kg (does not include the mould)
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Moisture content:
M w
w =
M s
where
w = moisture content in percent
Mw = mass of water in the moisture sample
Ms = mass of the dry moisture sample
Dry Unit Weight:
where
ρ
ρ d =
1
( + w)
ρd = the dry density of the soil
ρ = the wet density of the soil
Zero Air Voids:
where
REPORT:
=
G
x ρ
s
ρ d ZAV
w
1+
wGs
Gs = the specific gravity of the compacted soil (Assume it as 2.750)
ρw = the density of water (1000 kg/m 3 )
w = the moisture content of the soil
The report shall include:
1. Tabulated results obtained in the laboratory on the form posted on the website for both the
Standard and Modified test showing the calculated values for moisture content and dry density
and zero air voids dry density.
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2. Moisture density curves for each test showing the maximum density and the optimum moisture
content and ZAV curves plotted on two separate graphs; show only the three highest moisture
content values for the zero air voids curve.
3. On a separate graph plot both the Modified and Standard curves and a zero air voids curve.
4. In the conclusions compare the maximum densities and the optimum moisture contents obtained
in the two tests. Calculate the value of the ratio of the maximum dry densities:
Standard ρ
Modified ρ
d max
d max
5. Compare the shapes of the moisture density curves in terms of whether: a) the left hand (wet)
sides of the standard and modified curves parallel, b) the right hand (dry) sides are parallel to
each other and c) the left hand (wet) sides are parallel to the zero air voids curve?
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