AIM
To determine the maximum dry density and the optimum
moisture content of soil using heavy compaction as per IS: 2720
(Part 8) - 1983.
APPARATUS
CYLINDRICAL METAL MOULD
i) Cylindrical metal mould - it should be either of 100mm dia.
and 1000cc volume or 150mm dia. and 2250cc volume and
should conform to IS: 10074 - 1982
ii) Balances - one of 10kg capacity, sensitive to 1g and the
other of 200g capacity, sensitive to 0.01g
iii) Oven - thermostatically controlled with an interior of noncorroding material to maintain temperature between 105 and
110oC
iv) Steel straightedge - 30cm long
v) IS Sieves of sizes - 4.75mm, 19mm and 37.5mm
PREPARATION OF SAMPLE
A representative portion of air-dried soil material, large enough to
provide about 6kg of material passing through a 19mm IS Sieve
(for soils not susceptible to crushing during compaction) or about
15kg of material passing through a 19mm IS Sieve (for soils
susceptible to crushing during compaction), should be taken.
This portion should be sieved through a 19mm IS Sieve and the
coarse fraction rejected after its proportion of the total sample
has been recorded.
Aggregations of particles should be broken down so that if the
sample was sieved through a 4.75mm IS Sieve, only separated
individual particles would be retained.
PROCEDURE
A) Soil not susceptible to crushing during compaction –
i) A 5kg sample of air-dried soil passing through the 19mm IS
Sieve should be taken. The sample should be mixed
thoroughly with a suitable amount of water depending on the
soil type (for sandy and gravelly soil - 3 to 5% and for
cohesive soil - 12 to 16% below the plastic limit). The soil
sample should be stored in a sealed container for a
minimum period of 16hrs.
ii) The mould of 1000cc capacity with base plate attached,
should be weighed to the nearest 1g (W1 ). The mould
should be placed on a solid base, such as a concrete floor
or plinth and the moist soil should be compacted into the
mould, with the extension attached, in five layers of
approximately equal mass, each layer being given 25 blows
from the 4.9kg rammer dropped from a height of 450mm
above the soil. The blows should be distributed uniformly
over the surface of each layer. The amount of soil used
should be sufficient to fill the mould, leaving not more than
about 6mm to be struck off when the extension is removed.
The extension should be removed and the compacted soil
should be levelled off carefully to the top of the mould by
means of the straight edge. The mould and soil should then
be weighed to the nearest gram (W2).
iii) The compacted soil specimen should be removed from the
mould and placed onto the mixing tray. The water content
(w) of a representative sample of the specimen should be
determined as in Para 5.1.
iv) The remaining soil specimen should be broken up, rubbed
through 19mm IS Sieve and then mixed with the remaining
original sample. Suitable increments of water should be
added successively and mixed into the sample, and the
above operations i.e. Para ii) to iv) should be repeated for
each increment of water added. The total number of
determinations made should be at least five and the
moisture contents should be such that the optimum
moisture content at which the maximum dry density occurs,
lies within that range.
B) Soil susceptible to crushing during compaction –
Five or more 2.5kg samples of air-dried soil passing through the
19mm IS Sieve, should be taken. The samples should each be
mixed thoroughly with different amounts of water and stored in a
sealed container as mentioned in Para A) i), above. Follow the
operations given in Para A) ii) to iv), above.
C) Compaction in large size mould –
For compacting soil containing coarse material upto 37.5mm
size, the 2250cc mould should be used. A sample weighing
about 30kg and passing through the 37.5mm IS Sieve is used for
the test. Soil is compacted in five layers, each layer being given
55 blows of the 4.9kg rammer. The rest of the procedure is the
same as in Para A) or B), above.
REPORTING OF RESULTS
Bulk density γ in g/cc of each compacted specimen should be
calculated from the equation,
γ = (W2-W1)/V
where, V = volume in cc of the mould.
The dry density γ d in g/cc = 100γ/(100+w)
The dry densities, γ d obtained in a series of determinations
should be plotted against the corresponding moisture contents,
w. A smooth curve should be drawn through the resulting points
and the position of the maximum on the curve should be
determined. A sample graph is shown below:
The dry density in g/cc corresponding to the maximum point on
the moisture content/dry density curve should be reported as the
maximum dry density to the nearest 0.01.
The percentage moisture content corresponding to the maximum
dry density on the moisture content/dry density curve should be
reported as the optimum moisture content and quoted to the
nearest 0.2 for values below 5 percent, to the nearest 0.5 for
values from 5 to 10 percent and to the nearest whole number for
values exceeding 10 percent.