Geotechnical Engineering

DHARM

INDEX PROPERTIES AND CLASSIFICATION TESTS 81

∴ The weight of solid mixed in the suspension = 0.445 N.

By Eqs. 3.21 and 3.22,

D = K Ht/

where K =

3

1

μ

γ

w

w()G−

∴ K =

3 0 001

98 27 1

× 0 01342

×−

. =
.(. )

.mmmin

cm

.

∴ D = 0.01342 10 5

30

. mm = 0.00794 mm ≈ 0.008 mm

∴ The effective diameter corresponding to the 30-min, reading = 0.008 mm

By Eq. 3.34,

N =

G

G

V

W

. whR
()

γ ..

− 110

∴ N =

27

17

001 1000

0 445

12

10

.

.

.

.

×× × = 42.83

∴ The percentage of particles finer than 0.008 mm is 43.

Example 3.13: The liquid limit of a clay soil is 56% and its plasticity index is 15%. (a) In what

state of consistency is this material at a water content of 45%? (b) What is the plastic limit of

the soil? (c) The void ratio of this soil at the minimum volume reached on shrinkage, is 0.88.

What is the shrinkage limit, if its grain specific gravity is 2.71?

Liquid limit, WL = 56%

Plasticity index, Ip = 15%

Ip = wL – wp, by Eq. 3.37.

∴ 15 = 56 – wp

Whence the plastic limit, wp = (56 – 15) = 41%

∴ At a water content of 45%, the soil is in the plastic state of consistency.

Void ratio at minimum volume, e = 0.88

Grain specific gravity, G = 2.71

Since at shrinkage limit, the volume is minimum and the soil is still saturated,

e = wsG

or ws = e/G = 0.88/2.71 = 32.5%

∴ Shrinkage limit of the soil = 32.5%.

Example 3.14: A soil has a plastic limit of 25% and a plasticity index of 30. If the natural
water content of the soil is 34%, what is the liquidity index and what is the consistency index?
How do you describe the consistency?

Plastic limit, wp = 25%

Plasticity index, Ip = 30

By Eq. 3.37, Ip = wL – wp