Soil mechanics and its types

SOIL MECHANICS AND ITS TYPES
Presnted by
• R.KAVINKUMAR(16BCE3032)

WHAT IS SOIL?
 Soil is defined as the weathered and fragmented outer
layer (crust) of the earth’s terrestrial surface.

• Soil Mechanics is defined as the branch of engineering
science which enables an engineer to know
theoretically or experimentally the behavior of soil
under the action of
1. Loads (static or dynamic),
2. Gravitational forces,
3. Water and,
4. Temperature.

 Soil Mechanics is the branch of science that deals with study of
physical properties of soil and behavior of soil masses
subjected to various types of forces.
 Geotechnical Engineering is the sub discipline of Civil
Engineering that involves applications of the principles of Soil
Mechanics and Rock Mechanics to design of foundations,
retaining structures and earth structures.
Soil
Mechanics
GeoTech.
Engg.
Civil Engg.

 Karl Terzaghi has often been called the father of Soil
Mechanics.
 Academically, he earned an under graduate degree in
Mechanical Engineering.But he is also a civil engineer
and geologist

WHY WE STUDY SOIL MECHANICS?
 Virtually every structure is supported by soil or rock.
Those that aren’t either fly, float or fall over.
 Various reasons to study the properties of Soil:
1. Foundation to support Structures and Embankments
2. Construction Material
3. Slopes and Landslides
4. Earth Retaining Structures
5. Special Problems

FOUNDATION TO SUPPORT
STRUCTURES AND EMBANKMENTS

CONSTRUCTION MATERIAL
• Subgrade of highway pavement
• Land reclamation
• Earthen dam

• Engineering Soil Surveys
• Soil Sampling Devices and Methods
• Soil Testing Devices and Methods
• Physical Properties of Soil
• Evaluation and Interpretation of Test results
• Behavior under Loads and Forces
• Soil Conservation Techniques
• Sedimentation Control of Dam Reservoirs
• Design and Operation of Landfills

WEATHERING OF ROCKS
 PHYSICAL WEATHERING
 CHEMICAL WEATHERING
 ROCK CYCLE

 Weathering is the process of breaking down rocks by
physical and chemical process into smaller particles.
 Biological weathering is caused by activities of living
organisms - for example, the growth of roots or the
burrowing of animals. Tree roots are probably the most
occurring, but can often be by animals!

 Physical (or mechanical) Weathering is the disintegration
of rocks into smaller particles through physical processes,
including:

Chemical Weathering is the disintegration of rock through
chemical reactions between the minerals in the rocks,
water, and oxygen in the atmosphere.

All rock at or near Earth's surface is
being modified by the processes of
metamorphism, melting,
crystallization, lithification and
weathering.

TYPES OF SOILS
 FORMATION OF SOIL
 TYPES OF SOIL
 Geological Consideration
 Engineering Consideration

FORMATION OF SOIL
 Soil is generally formed by disintegration and decomposition
(weathering) of rocks through the action of physical (or mechanical)
and chemical agents which break them into smaller and smaller
particles.

TYPES OF SOIL
 Soil types, based on geological and engineering view
points, are separately discussed below:
1. Geological consideration:
Geologist classify soil into two major categories: residual
soils and transported soil
i. Residual Soils:
When the rock weathering is faster than the transport process
induced by water, wind and gravity, much of the soil remains in
place. It is known as residual soil.

TYPES OF SOIL
ii. Transported Soil:
• Glacial Soil: This type of soil is developed, transported and deposited
by the actions of glaciers. These deposits consists of rocks fragments,
boulders, gravels, sand, silt and clay in various proportions (i.e., a
heterogeneous mixture of all sizes of particles).
• Alluvial Soil: This type of soil (also known as fluvial soil or alluvium) is
transported and deposited to their present position by streams and
rivers.
Coarser or
Heavier
Particles
Higher
Reaches
Fine
Particles
Lower
Reaches

TYPES OF SOIL
iii. Aeolian Soil: The soil transported by geological agent ‘wind’ and
subsequently deposited is known as wind blown soil or Aeolian Soil.
iv. Colluvial Soil: A colluvial soil is one transported downslope by gravity.
There are two types of downslope movement – slow (creep – mm/yr)
and rapid (e.g., landslide)
v. Lacustrine and Marine Soil:
• Lacustrine Soil is deposited beneath the lakes.
• Marine Soil is also deposited underwater i.e., in the Ocean.

TYPES OF SOIL
2. Engineering consideration:

TYPES OF SOIL
• Engineering consideration:
• Clay: ( < .002mm)
• In moist condition, clay becomes sticky and can be rolled into threads.
• High dry strength, low erosion, low permeability, good workability and compaction
under moist condition. Also susceptible to shrinkage and swelling.
• Sand: (.06mm < Size < 2mm)
• Particle shape varies from rounded to angular
• No plasticity, considerable frictional resistance, high permeability and low capillarity
• Abundant quantities of sand are available in deserts and riverbeds

TYPES OF SOIL
2. Engineering consideration:
• Gravels: (2mm < Size < 60mm)
• They form a good foundation material.
• The gravels produced by crushing of rocks are angular in shape while those
taken from riverbeds are sub-rounded to rounded.
• Cobbles and Boulder:
• Particles larger than gravels are commonly known as cobbles and boulders.
• Cobbles generally range in size 60mm t0 200mm.
• The materials larger than 200mm is designated as boulders.

Soil mechanics and its types

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