Geotechnical Engineering

DHARM

INDEX PROPERTIES AND CLASSIFICATION TESTS 67

By analysing the conditions of the soil pat at the initial stage, at the stage of shrinkage
limit, and at the completely dry state, one can arrive at an expression for the shrinkage limit
as follows (Fig. 3.20):

V

Solids

Wi

Water

Solids

Vm Wm

Air

Solids

Vd

Vs

WWds»

(i) Initial stage of soil pat

Water

(ii) Soil pat at shrinkage limit (iii) Dry soil pat

Fig. 3.20 Determination of shrinkage limit

Weight of water initially = (Wi – Wd)

Loss of water from the initial stage to the

stage of shrinkage limit = (Vi – Vm)γw

∴ Weight of water at shrinkage limit = (Wi – Wd) – (Vi – Vm)γw

∴ Shrinkage limit, ws =

()()WW VV

W

id imw

d

L −−−

N

M

O

Q

P

γ

× 100% ...(Eq. 3.47)

or ws = w

VV

i W

idw

d

− −

L

N

M

O

Q

P

()γ

× 100% ...(Eq. 3.48)

where wi = initial water content

Vi = initial volume of the soil pat
Vd = Vm = dry volume of the soil pat
Wd = dry weight of the soil sample
This equation suggests a laboratory method for the determination of the shrinkage limit.
The equipment or apparatus consists of a porcelain evaporating dish of about 12 cm
diameter with float bottom, a shrinkage dish of stainless steel with flat bottom, 45 mm in
diameter and 15 mm high, two glass plates, each 75 mm × 75 mm, 3 mm thick—one plain
glass, and the other with three metal prongs, glass cup 50 mm in diameter and 25 mm high,
with its top rim ground smooth and level, straight edge, spatula, oven, mercury desiccator,
balances and sieves. (Fig. 3.21)(IS: 2720, Part VI–1972).

If the test is to be made on an undisturbed sample, it is to be trimmed to a pat about
45 mm in diameter and 15 mm in height. If it is to be conducted on a remoulded sample, about
1 N of a thoroughly mixed portion of the material passing 425–μ–IS sieve is to be used.

The procedure is somewhat as follows:
The volume of the shrinkage dish is first determined by filling it with mercury, remov-
ing the excess by pressing a flat glass plate over the top and then weighing the dish filled with
mercury. The weight of the mercury divided by its unit weight (0.136 N/cm^2 ) gives the volume
of the dish which is also the initial volume of the wet soil pat (Vi). The inside of the dish is