Geotechnical Engineering

DHARM

SOIL AND SOIL MECHANICS 9

1.7.3 Flocculent Structure

This structure is characteristic of fine-grained soils
such as clays. Inter-particle forces play a predomi-
nant role in the deposition. Mutual repulsion of the
particles may be eliminated by means of an appro-
priate chemical; this will result in grains coming
closer together to form a ‘floc’. Formation of flocs is
‘flocculation’. But the flocs tend to settle in a honey-
comb structure, in which in place of each grain, a
floc occurs.

Thus, grains grouping around void spaces
larger than the grain-size are flocs and flocs group-
ing around void spaces larger than even the flocs
result in the formation of a ‘flocculent’ structure.

Very fine particles or particles of colloidal size
(< 0.001 mm) may be in a flocculated or dispersed
state. The flaky particles are oriented edge-to-edge
or edge-to-face with respect to one another in the
case of a flocculated structure. Flaky particles of
clay minerals tend to from a card house structure
(Lambe, 1953), when flocculated. This is shown in
Fig. 1.5.

When inter-particle repulsive forces are
brought back into play either by remoulding or by
the transportation process, a more parallel arrange-
ment or reorientation of the particles occurs, as
shown in Fig. 1.6. This means more face-to-face con-
tacts occur for the flaky particles when these are in
a dispersed state. In practice, mixed structures oc-
cur, especially in typical marine soils.

1.8 Texture of Soils

The term ‘Texture’ refers to the appearance of the surface of a material, such as a fabric. It is
used in a similar sense with regard to soils. Texture of a soil is reflected largely by the particle
size, shape, and gradation. The concept of texture of a soil has found some use in the classifica-
tion of soils to be dealt with later.

1.9 Major Soil Deposits of India

The soil deposits of India can be broadly classified into the following five types:

1. Black cotton soils, occurring in Maharashtra, Gujarat, Madhya Pradesh, Karnataka,
   parts of Andhra Pradesh and Tamil Nadu. These are expansive in nature. On account of

Fig. 1.4 Flocculent structure

Fig. 1.5 Card-house structure of

flaky particles

Fig. 1.6 Dispersed structure