UNIT-1 INTRODUCTION & SOIL PHASE RELATIONSHIPS

1. GEO-TECHNICAL ENGINEERING
UNIT-1
INTRODUCTION
K.MANOJ KUMAR
LECTURER

2. SOIL FORMATION
Soil is formed by the process of ‘Weathering’ of rocks and
decomposition of organic matter.
Formation of soil
Weathering of rocks Decomposition of organic matter
Physical Chemical
Ex:- Peat, Humus,
Muck etc

3. Physical Weathering:-
➢ The breakdown of rocks and minerals into smaller pieces
without a change in its chemical composition.
➢ It is due to the physical effects like temperature, abrasion,
wedging action of ice, penetration of plant roots etc.
➢ It produces coarse grained and non cohesive soils
➢ Example:- Gravel, Sands

4. Chemical Weathering:-
➢ It is due to the chemical actions ( oxidation, hydration,
carbonation, solution, leaching etc)
➢ It results in the chemical composition of the particles.
➢ It results in fine grained and cohesive soils.
➢ Examples:- Clays and silts

5. The formation of soil is a ‘pedogenesis process’, which is
also called as ‘geological cycle’.
GeologicalCycle

6. TYPES OF SOILS
1. Based on the place of origin
a) Residual soils
b) Transported soils
2. Based on the grain size
a) Coarse grained soils
b) Fine grained soils

7. Residual soils:-
• Soils that remain at the location of its formation.
Transported soils:-
• Soil that are transported from its place of origin by wind,
water or glacier.
• Further subdivided depending upon transporting agency.

8. Some other different soils commonly used:-
Bentonite:- Decomposed volcanic ash
containing a high percentage
of clay mineral – montmorillonite.
It exhibits high shrinkage and swelling.
Black cotton soil:- It is a residual soil
formed from the basalt trap having
very low bearing capacityand high
swelling and shrinkage characteristics.
Boulder clay:- Glacial clay containing all
sizes of rock fragments from boulders
down to finely pulverized clay materials.

9. Caliche:- Soil conglomerate of gravel, sand
and clay cemented by calcium carbonate.
Hard pan:- Densely cemented soil which
remains hard when wet.
Laterite:- This is red or deep brown soil in
colour due to the presence of iron oxide.
Loam:- Mixture of sand, silt and clay size
particles.

10. Loess:- Uniform wind blown yellowish
brown silt or silt clay.
Morrum:- Morrum means the powdered
rock, when gravel is mixed with the red
clay morrum is formed.
Top soil:- Surface materials which supports
plant life.
Oragnic soils:- Formed by the growth and
subsequent decomposition of plants.
EX:- Peat, Muck, Humus etc

11. SOIL STRUCTURE
• The arrangement of soil particles and their aggregate into
certain defined patterns is called soil structure.
• The primary soil particles i.e. sand ,silt and clay – usually
grouped together in the form of aggregates.
Types of structure:-
1. Single Grained Structure
2. Honey-comb Structure
3. Flocculent Structure

12. Single Grained Structure:-
• Single grained structure is characteristic of coarse grained soils
with a particle size greater than 0.02 mm.
• Single grained structures are present in cohesion less soils like
gravel and sand.
• Gravitational forces predominate the surface forces and hence
grain to grain contact results.
• The deposition in loose state - with largevoids
dense state – with less voids

13. Honey - comb Structure:-
• This structure can occur only in fine-grained soils, especially in silt .
• Due to the relatively smaller size of grains, besides gravitational forces,
inter-particle surface forces also play an important role in the process
of settling down.
• Miniature arches are formed, which bridge over relatively large void
spaces. This results in the formation of a honey-comb structure, each
cell of a honey-comb being made up of numerous individual soil
grains.
• The structure has a large void space and may carry high loads without
a significant volume change.
• The structure can be broken down by external disturbances.

14. Flocculent Structure:-
• This structure is characteristic of fine-grained soils such as
clays. Inter-particle forces play a predominant role in the
deposition.
• In this grains comes 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 grouping around
void spaces larger than even the
flocs result in the formation of a
‘flocculent’ structure.

15. • 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.
• When inter-particle repulsive forces are
brought back into play either by remoulding
or by the transportation process, a more
parallel arrangement or reorientation of the
particles occurs, as shown in fig.
This means more face-to-face contactsoccur
for the flaky particles when these are in a dispersed state.

16. SOIL PHASE RELATIONSHIPS
• Soil mass is generally a three-phase system.
• It consists of solid particles, liquid, and gas.
• For all practical purposes, the liquid may be considered to be
water (although in some cases, the water may contain some
dissolved salts) and the gas as air.
• The phase system may be expressed in SI units either in terms
of mass-volumeor weight-volume relationships.
• The interrelationships of the different phases are important
since they help to define the condition or the physical make-
up of the soil.

17. Phase relationship diagram:-
• In a mass of soil, there are three physical components:
solid, water, and air.
• A phase relationship diagram is normally used to
represent the relationship as follows:
Partially saturated soil (Three-phase system)General representationof soil

18. When the soil voids are completely filled with water, the gaseous
phase being absent, it is said to be ‘Fully Saturated soil’ .
When there is no water at all in the voids, the voids will be with
air, the liquid phase being absent, the soil is said to be ‘Dry soil’.
In both these cases, the soil system reduces to a ‘two phase
system’ as shown in below fig.
Fully saturatedsoil (Two-phase system) Dry soil (Two-phase system)

19. Basic Terminology:-
A number of quantities or ratios are defined below which
constitutes thebasic terminology in the soil mechanics.
Three-phase system of soil

20. Weight– volume relationships:-
Volume relations:-
Void ratio (e):- It is the ratio of the volume of voids (Vv) to the volume
of soil solids (Vs).
Porosity (n):- It is the ratio of the volume of voids to the total volume
of soil (V ), and is expressed as a percentage.
Degree of saturation (S) :- It is the ratio of volume of water(Vw) the
volume of voids(Vv). This can be expressed as the in percentage.
For a dry soil, S = 0%, and for a fully saturatedsoil, S = 100% or 1.
e fine grained soils > e coarse grainedsoils
Range:- 0 < n < 100%
Range:- 0 % ≤ S ≤ 100%

21. Air content (ac):- It is the ratio of the volume of air (Va) to the volume of
voids (Vv) .
Percentage air voids (na):- It is the ratio of the volume of air (Va) to the
total volume (V).
Range:- 0 ≤ ac ≤ 100%
Range:- 0 ≤ na < 100%

22. Weight relations:-
The common terms used for weight/mass relationships are moisture
content and unit weight.
Water content (w):-The ratio of the weight of water (Ww) present to the
weight of solid particles (Ws). Also called as moisture content.
Unit weight(ϒ):-It is defined as the weight of soil per unit volume.
units:- KN/ m3
unit weight of water = 9.81 KN/ m3
Bulk Unit weight(ϒ):- It is defined as the total weight(W) of a soil per unit
of its total volume(V).

23. Dry unit weight (ϒ d):- it is defined as the weight of soil solids (WS) to
the total volume of given soil mass(V).
Unit weight of solids (ϒ S):- It is the ratio of weight of soil solids (WS) to
the volume of solids(VS).
Saturated unit weight (ϒ Sat):- It is the ratio of total weight of fully
saturated soil sample (WSat) to its total volume of soil mass(V).

24. Submerged unit weight (ϒ ‘):- It is the ratio of the submerged weight
of soil solids (WS ) sub to the total volume of soil(V).
Specific Gravity (G or GS):- It is the ratio of unit weight of solids to
that unit weight of water at 4oc.

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