Determination of maximum dry density and optimum moisture content of soil using heavy compaction according to IS: 2720 (Part 8) - 1983.
Apparatus Required:
1. Cylindrical metal mould
- it should be 100 mm diameter and 1000cc volume or 150mm diameter and 2250cc
volume corresponding to IS: 10074 - 1982
2. Balances - one of 10
kg capacity, sensitive to 1 g and hence another 200 g capacity, sensitive to
0.01 g.
3. Oven - Thermostatically controlled with an indoor non-corrosive material to take care of temperatures between 105 and 110℃.
4. Steel straight edge
- 30 cm long
5. IS Size - 4.75 mm,
19 mm and 37.5 mm
Sample
Preparation:
A representative
portion of the air-dried soil material, which is sufficient to supply about 6
kg of material to pass through a 19 mm IS sieve (the soil is not vulnerable to
crushing during condensation) or through a 19 mm IS sieve about 15 kg of material
passing through (susceptible to crushing during condensation), must be taken.
This part must be sieved through a 19 mm IS sieve and therefore the coarse
fraction is rejected after the proportion of the entire sample.
The aggregation of
particles must be broken down in the order that if the sample was sieved
through a 4.75 mm IS Sieve, only individual particles would be retained.
Procedure:
A)
Soil not susceptible to crushing
during compaction or Soil is not weak during compaction
-
i) A 5 kg sample of
air-dried soil passing through a 19 mm IS sieve should be taken. The sample
should be thoroughly mixed with the appropriate amount of water.
Soil type (for sandy
and gravel soils - 3 to 5 % and for cohesive soils - 12 to 16% below the
plastic limit). The soil sample should be stored for a minimum period of 16hrs within
the sealed container.
ii) A 1000cc capacity
mould should be attached to the base plate, weighing 1g (W1) to the
nearest. The mould should be placed on a concrete base, like a concrete floor or
plinth and therefore moist soil should be deposited and compacted in the mould,
with extension fixed, in five layers of approximately equal mass, each layer
being given 25 blows.
The 4.9 kg rammer fell
from a height of 450 mm from the soil. Blows should be distributed evenly over
the surface of each layer. Amount of soil used should be sufficient to fill the
mould,leaving less than about 6 mm when the extension is removed. The extension
must be removed and therefore compacted soil must be carefully sealed through
the straight edge to the highest level of mould. The mould and soil is weighed
to the nearest gram (W2).
iii) Compact soil
samples should be removed from the mould and placed on a blending tray. The representative
sample of the specimen’s water content should be determined as well.
iv) The remaining soil
sample should be rubbed and sliced through a 19 mm IS sieve, then mixed with
the remaining original sample. Appropriate increments of water should be added
sequentially and mixed into the sample, and therefore the operations performed
above (ii) to (iv) should be repeated for each increment of added water. The
total number of determinations made must be a minimum of five and therefore the
moisture content must be such an optimum moisture at which the maximum dry
density lies within the range.
B)
Soil susceptible to crushing during
compaction or Soil during compaction of soil -
Five or more 2.5 kg
samples of air-dried soil passing through a 19 mm IS sieve should be taken.
Samples must be mixed with varying amounts of water in each well and stored
during a seal container as described in (para A)(i), above.
Follow the operations
given in para A (ii) to (iv), above.
C)
Compaction in large size mould -
To deposit soil
containing coarse material up to 37.5 mm size, a 2250cc mould should be used. A
specimen weighing approximately 30 kg passing through the 37.5 mm IS Sieves should
be employed for testing. The soil is compacted into five layers, each layer is
given 55 blows of the 4.9 kg rammer. The remainder of the procedure is similar
to Para (A) or( B) above.
Result:
The bulk density γ
in g/cc of each compacted sample should be calculated from
the equation
γ = (W2-
W1) / V
Where, V = volume in
the cc of the mould.
Dry density γd in g/cc = 100γ / (100+ w)
The dry density γd, obtained during a
series of determination, should be plotted against the corresponding moisture
content, w. A smooth curve must be drawn through the resulting points and hence
the position of the maximum on the curve must 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 nearest to 0.01 as the maximum dry density.
The percent moisture
content corresponding to the maximum dry density on the moisture content / dry
density curve should be reported as the optimal moisture content and quoted for
the nearest 0.2 for values below 5%, 5 to 10 percent,to values closest to 0.5.
Nearest whole number for values greater than 10 percent.
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