Different types of soil structure

1. INTRODUCTION SOIL STRUCTURE

2. INTRODUCTION TO GEOTECHNICAL
ENGINEERING:
 Geotechnical Engineering is a term which includes Soil Mechanics,
Rock Mechanics and Geology.
 Soil Mechanics deals with action of forces on soil and with flow of
water on soil.
 Rock Mechanics deals with mechanics of rock.
 Geology deals with the study of Earth, the rocks of which it is
composed, and the processes by which they change.
 Out of the above 3, we mainly deal with Soil Mechanics for this
course.

3. APPLICATIONS TO CIVIL ENGINEERING:
A) Foundations:
 Every civil engineering structure – building or bridge or dam, it is
founded on or below the surface of earth.
 Foundations are required to transmit the load of the structure safely to
the soil.
 Foundation Engineering is an important branch in Geotechnical
Engineering.

5. B) Retaining Structures:
 When sufficient space is not available for a mass of soil to spread and
form a safe slope, a structure is required to retain the soil.
 Geotechnical Engineering gives the theories of Earth Pressure on
retaining structures.

6. C) Slope Stability:
 Whether natural slope or man nade slope – to prevent landslides,
slope stability is important.
 Geotechnical Engineering provides methods to check stability of
slopes.

7. D) Pavement Design:
 A pavement is a hard crust placed on soil for the purpose of providing
a smooth and strong surface on which the vehicles can move.
 Pavement consists of subgrade, sub base course, base course and
surface course.
 Behaviour of subgrade on various loading and environmental
conditions are studied in Geotechnical Engineering.
PAVEMENT DETAILS

8. COMPLEXITY OF SOIL STRUCTURE:
 Soil is a highly complex material.
 It differs from conventional structural materials such as steel and
concrete.
 Properties of steel can be accurately controlled and properties of
concrete can be controlled to some extent during its preparation.
 Soil is a material which has been subjected to changes of nature and
we cannot control that.
 Thus, soil is a heterogeneous and unpredictable material.
 Properties of soil also change with change in environmental, loading
and drainage conditions.
 Main engineering properties of steel and concrete are Elastic Modulus
(stress/strain), Tensile strength and Compressive Strength.
 Most of the design work can be done if these above properties are
known.

9.  However, engineering properties of soils depend on a lot of factors and
it is not possible to characterize them by 2 or 3 parameters.
 Detailed testing is required to determine the characteristics of soil and
only then design can be done.
 Steel and concrete can be inspected before use, soils for foundations
are at great depth and not open to inspection.
MAJOR SOIL DEPOSITS OF INDIA:
Soil deposits of India can be classified into 5 major groups.
A) Alluvial Soil:
 A large part of North India is covered with Alluvial soils.
 The distinct characteristics of Alluvial deposits is the existence of
alternating layers of sand, silt and clay.
 Thickness of each layer depends on the local terrain and nature of
floods in the rivers causing deposition.

10. B) Black Cotton Soil:
 A large portion of central India and a portion of South India are
covered with Black Cotton Soils.
 These soils are residual deposits formed from basalt rocks.
 These soils are clays of high plasticity.
 They have high shrinkage and swelling properties.
 Shear strength, Bearing capacity of this soil are extremely low.
C) Laterite Soil:
 Laterite soils are formed by decomposition of rock, removal of bases
and silica and accumulation of Iron oxide and Aluminium oxide.
 Presence of Iron oxide gives these soils the characteristic red or pink
colour.
 These are residual soils formed from basalt.
(Basalt: Most common type of solidified lava; a dense dark grey fine-
grained igneous rock)

11.  These soils exist in Central, Southern and Eastern India.
 These are soft and can be cut with a chisel when wet but they become
hard as time passes.
D) Desert Soil:
 A large part of Rajasthan and adjoining states is covered with sand
dunes.
 In this area, arid conditions exist with little rainfall. (Arid: No water)
 Size of the particles is in the range of fine sands.
 They are uniform in gradation.
 (Gradation): Proportion of material of each grain size present in a soil.
E) Marine Soil:
 They contain a large amount of organic matter.
 They are present along the coast.
 They have very low shear strength, highly plastic,highly compressible.

12. FIELD IDENTIFICATION OF SOILS:
Cohesion:
It is the bonding force or attractive fore between the particles of fine
grained soils that creates shear strength.
Sizes of soil:
Gravel – Between 80 mm and 4.75 mm.
Sand – Between 4.75 mm and 75 microns.
Silt – Between 75 microns and 0.002 mm.
Clay – Finer than 0.002 mm.

13. Thank You