Geotechnical Engineering

DHARM

INDEX PROPERTIES AND CLASSIFICATION TESTS 71

Sr =

()VV

V

id

i

−

× 100 ...(Eq. 3.59)

The only difference between this and the volumetric shrinkage is in the denominator,

which is the initial volume in this case.

Schedig classifies the soil qualitatively based on its degree of shrinkage as following:

Good soil ... Sr < 5%

Medium soil ... Sr – 5 to 10%

Poor soil ... Sr – 10 to 15%

Very poor soil ... Sr > 15%

Linear Shrinkage (Ls)

‘Linear Shrinkage (Ls)’ is defined as the decrease in one dimension of the soil mass

expressed as a percentage of the initial dimension, when the water content is reduced from a

given value to the shrinkage limit. This is obtained as follows:

Ls = 1

100

100

−^3

+

F

HG

I

Vs KJ

× 100 ...(Eq. 3.60)

Shrinkage Limit of Undisturbed Soil (wsu)

The shrinkage limit of undisturbed soil speciman is obtained as follows:

wsu = V

WG

du

du

−

F

HG

I

KJ

(^1) × 100 ...(Eq. 3.61)
where Vdu and Wdu are the volume in ml and weight in g, respectively, of the oven-dry soil
specimen.

Activity of Clays

The presence of even small amounts of certain clay minerals can have significant effect on the

properties of the soil. The identification of clay minerals requires special techniques and equip-

ment. The techniques include microscopic examination, X-ray diffraction, differential thermal

analysis, optical property determination and electron micrography. Even qualitative identifi-

cation of the various clay minerals is adequate for many engineering purposes. Detailed treat-

ment of clay minerals is considered out of scope of the present text.

An indirect method of obtaining information on the type and effect of clay mineral in a

soil is to relate plasticity to the quantity of clay-size particles. It is known that for a given

amount of clay mineral the plasticity resulting in a soil will vary for the different types of

clays.

‘Activity (A)’ is defined as the ratio of plasticity index to the percentage of clay-sizes:

A =

I

c

p ...(Eq. 3.62)

where c is the percentage of clay sizes, i.e., of particles of size less than 0.002 mm.

Activity can be determined from the results of the standard laboratory tests such as the
wet analysis, liquid limit and plastic limit. Clays containing kaolinite will have relatively low
activity and those containing montmorillonite will have high activity.