Geotechnical Engineering

DHARM

INDEX PROPERTIES AND CLASSIFICATION TESTS 69

Substituting γd =

G

e

. w
()

γ

1 +

in Eq. 3.46,

ws =

()11+

−=

e

GG

e

G

...(Eq. 3.51)

where e is the void ratio of the soil at its minimum volume. (This also indicates that the soil is
still saturated at its minimum volume). Initial wet weight and initial wet volume are not
required in this approach.

Another alternative approach is to determine the weight and volume of the soil pat at a
series of decreasing moisture contents using air-drying (and ultimately oven-drying to obtain
the values in the dry state) and plotting the volume observations against the moisture contents
as follows (Fig. 3.22):

The straight line portion of the curve is produced to meet the horizontal through the
point representing the minimum or dry volume. The water content corresponding to this meeting
point is the shrinkage limit, ws. However, this approach is too laborious.

45°

Volume change of soil pat

Ws Water content %

Fig. 3.22 Water content vs volume soil pat

Approximate Value of G from Shrinkage Limit

The approximate value of G may be got from this test as follows:

γs = G. γw =

W

V

W

V

s

s

d

s

=

or G =

W

V

d

swγ

.

From Fig. 3.20 (i),

Vs = Vi –

()WWid

w

−

γ

∴ G =

W

VWW

d

iwγ− −()i d

...(Eq. 3.52)