Geotechnical Engineering

DHARM

COMPACTION OF SOIL 431

Enough water should be added to the specimen to bring its moisture content to about

7% (sandy soils) and 10% (clayey soils) less than the estimated optimum moisture content. The

processed soils should be kept in an airtight tin for about 18 to 20 h to ensure thorough mixing

of the water with the soil.

The wet soil shall be compacted into the mould in three equal layers (five equal layers

for heavy compaction), each layer being given 25 blows if the 100 mm diameter mould is used

(or 56 blows if the 150-mm diameter mould is used) from the rammer weighing 26 N dropping

from a height of 310 mm (from the rammer weighting 48.9 N dropping from a height of 450

mm, for heavy compaction).

The rest of the procedure and usual precautions are as for other compaction tests (for

full details, vide the relevant IS Code).

Correction for oversize fraction may be applied as follows:

If the material retained on 20-mm IS Sieve (or 4.75 mm IS Sieve) has been excluded

from the test, the following corrections shall be applied for getting the values of maximum dry

density and optimum moisture content for the entire soil. For this purpose, the specific gravity

of the portion retained and passing the 20-mm. IS Sieve or the 4.75 mm IS Sieve, as the case

may be, should be determined separately.

Corrected maximum dry density =

γγ

γγ

sd

nnds

max

(^12) max+.
...(Eq. 12.1)
Corrected optimum moisture content = n 1 A 0 + n 2 w 0 ...(Eq. 12.2)
where γs = unit mass of oversize gravel particles in kN/m^3 (= G. γw, where G is the specific
gravity of gravel particles);
γdmax = maximum dry density obtained in the test in kN/m^3 ;
n 1 = fraction by mass of the oversize particles in the total soil expressed as ratio;
n 2 = fraction by mass of the portion passing 20-mm IS Sieve (or 4.75 mm IS Sieve)
expressed as the ratio of total soil;
A 0 = water absorption capacity of oversize material, if any, expressed as percentage of
water absorbed, and
w 0 = optimum moisture content obtained in the test.
(This formula is based on the assumption that the volume of a compacted portion pass-
ing a 20-mm sieve (or a 4.75-mm sieve) is sufficient to fill the voids between the oversize
particles).
12.5.4Harvard Miniature Compaction Test
The compaction in this test is achieved by ‘kneading action’ of a cylindrical tamper 12.7 mm in
diameter. The mould is 33.34 mm in diameter and 71.53 mm in height and has a volume of
62.4 cm^3. The tamper operates through a present compression spring so that the tamping force
is controlled not to exceed a certain predetermined value. For different soils and different
compactive efforts desired, the number of layers, number of tamps per layer and the tamping
force may be varied.