Geotechnical Engineering

DHARM

COMPACTION OF SOIL 439

6. Improves bearing power and settlement Improves bearing power and settlement
   characteristics characteristics


7. Relatively quick process Relatively slow process


8. Relatively complex phenomenon involving Relatively simple phenomenon
   expulsion, compression, and dissolution of
   pore air-in water


9. Useful primarily in embankments and Useful as a means of improving the
   earth dams properties of foundation soil

12 .9 Illustrative Examples

Example 12.1: An earth embankment is compacted at a water content of 18% to a bulk den-

sity of 19.2 kN/m^3. If the specific gravity of the sand is 2.7, find the void ratio and the degree of

saturation of the compacted embankment. (S.V.U.—B.Tech. (Part-time)—Sept, 1983)

Water content, w = 18%

Bulk density, γ = 19.2 kN/m^3

Specific gravity, G = 2.7

Dry density, γd =

γ

()

.

1 (.)

19 2

+ 1018

=

w +

= 16.27 kN/m^3

But γd =

G

e

. w
()

,

γ

1 + where γw 9.81 kN/m

3

∴ (1 + e) =

27 981

16 27

..

.

×

= 1.63

Void ratio, e = 0.63

Also, wG = S.e

∴ The degree of saturation, S =

wG

e

=

018 27×

063

..
.
= 0.7714
∴ The degree of saturation = 77.14%
Example 12.2: A moist soil sample compacted into a mould of 1000 cm^3 capacity and weight
35 N, weighs 53.5 N with the mould. A representative sample of soil taken from it has an
initial weight of 0.187 N and even dry weight of 0.1691 N. Determine (a) water content, (b) wet
density, (c) dry density, (d) void ratio and (e) degree of saturation of sample.

If the soil sample is so compressed as to have all air expelled, what will be the new
volume and new dry density? (S.V.U.—Four year B.Tech.—Sept., 1983)

(a) Water content, w = (.. )

.

0 1870 0 1691

0 1691

100

−

× = 10.58%

Wet wt. of soil in the mould = (53.50 – 35.00) = 18.50 N

Volume of mould = 1000 cm^3