This document provides an introduction to geotechnical engineering and soil mechanics. It defines soil and discusses the branches of civil engineering related to soil, including foundation engineering. The document then discusses the history and development of soil engineering, from early uses of soil as a construction material through the classical and modern eras. It outlines key figures and their contributions, particularly highlighting Karl Terzaghi's role in establishing modern soil mechanics. The document also covers the scope of geotechnical engineering, including applications in foundation design, retaining structures, slope stability, pavement design, and earth dam design. It concludes with some limitations of geotechnical engineering given soil properties can vary significantly by location.

1. Introduction to Geotechnical
engineering
Mr. N. J. Hindocha

2. Introduction to Soil
• As per Civil engineering, soil may be defined
as an uncemented or weakly cemented
gathering of mineral particles which are
produced by the disintegration (weathering) of
rocks.
• The term foundation engineering is a branch
of civil engineering, which is associated with the
design, construction, maintenance and
renovation of footings, foundation walls, pile
foundation and all other structural members
which form the foundation of buildings and
other engineering structures.

3. WHAT IS “SOIL”?
• Soil is the mixture of minerals, organic matter,
gases, liquids, and the countless organisms
that together support life on Earth.
• Soil is considered to be the ―skin of the Earth‖.
• It includes widely different materials like sand,
gravels, clays and silts.
• The type of soil depend upon the size of
particles i.e. sandy soil, loamy soil, etc and on
the color of soil i.e. yellow soil, black soil, etc.

4. • Soil Engineering, Soil Mechanics or
Geotechnics is one of the youngest disciplines
of civil egg. involving the study of soil, its
behavior and applications as an engineering
material.
• Soil mechanics is a branch of engineering
mechanics that describes the behavior of soils.
• Soil mechanics is used to analyze the
deformations of and flow of fluids within natural
and man-made structures that are supported on
or made of soil, or structures that are buried in
soils.
• It is useful for building and bridge foundations,
retaining walls, dams, and buried pipeline
systems, etc.

5. HISTORY OF SOIL ENGINEERING
• Beginning of use of soil in pre-historic time..
• For Habitation, roads, etc.
• As a construction material.
• Fundaments of foundations & roads from the
trial and error experience.
• Use of ‗timber + stone caissons‘ of soft ground
shaft construction was known in Egypt in 2000
B.C.

6. • Began:
• 18th century since then, the science of Soil
• mechanics has evolved through 4 phases…
• Pre-classical (1700 A.D. to 1776 A.D.)
• Classical phase-1 (1776 A.D. to 1856 A.D.)
• Classical phase-2 (1856 A.D. to 1910 A.D.)
• Modern (1910 A.D. to present)

7. SOIL ENGINEERING PRIOR TO
THE 18TH CENTURY
• The record of the first use of soil as a
construction material by mankind is lost in
antiquity. In true engineering sense, there is no
‗Soil Engineering‘ prior to the 18th Century.
• For years, the art of Soil engineering and
Geotechnical engineering was based on only
past experiences through a succession of
experimentation without any real scientific
character.
• Based on those experimentations, many
structures were built—some of which have
crumbled, while others are still standing.

8. • One of the most famous examples
of problems related to soil bearing
capacity and foundations in the
construction of structures prior to
18th century is the Leaning Tower
of Pisa in Italy. The construction of
the Tower began in 1173 and last
over 200 years.
• The tower has tilted in the past to
the east, north, west and, finally,
to the south.
• Recent investigations showed that
a weak clay layer exists at a depth
of about 11 m below the ground
surface compression, which
caused the tower to tilt.

9. PRE-CLASSICAL PERIOD OF SOIL
MECHANICS
• This period concentrated on studies relating to
natural slope and unit weights of various types of
soils, as well as the semi empirical earth pressure
theories.
Henri Gautier (1660–1737)
studied the natural slopes of
soils when tipped in a heap for
formulating the design
procedures of retaining walls.

10. • Bernard Forest de Belidor (1671–1761 French
egg.) proposed a theory for lateral earth
pressure on retaining walls specified a soil
classification system.

11. CLASSICAL SOIL MECHANICS
• Classical Soil Mechanics began
in 1773 with Charles Coulomb‘s
(a physicist, 1736– 1806)
introduction of mechanics to
soil problems. Using the laws of
friction and cohesion to
determine the true sliding
surface behind a retaining wall,
Coulomb inadvertently defined
failure criteria for soil.
• By combining Coulomb's
theory with Christian Otto
Mohr‘s theory of a 2D stress
state, the Mohr Coulomb theory
was developed.

12. Joseph Boussinesq,
a mathematician and
physicist (1842-1929),
developed the theory
of stress distribution.
Henry Darcy (1803–
1858) defined the
Hydraulic conductivity.

13. William Rankines (1820–
1872) Simplified Coulomb's
earth pressure theory.
Osborne Reynolds
(1842– 1912)
demonstrated the
phenomenon of
dilatency in sand

14. MODERN SOIL MECHANICS
• This period was marked
by a series of important
studies and publications
related to the mechanic
behaviour of clays.
• Albert Atterberg (1846–
1916), a Swedish chemist
and soil scientist,
explained the consistency
of cohesive soils by
defining liquid, plastic, and
shrinkage limits.

15. • Arthur Bell (1874–1956), a
civil engineer from England,
developed relationships for
lateral pressure and
resistance in clay as well as
bearing capacity of shallow
foundations in clay.
• Wolmar Fellenius (1876–
1957), an engineer from
Sweden, developed the
stability analysis of saturated
clay slopes.
• Karl Terzaghi (1883–1963), a
civil engineer and geologist
from Austria, developed the
theory of consolidation for
clays as we know today..
Wolmar Fellenius

16. • The development of modern Geotechnical
Engineering as a branch of Civil Engineering is
absolutely impacted by one single professional
individual – Karl Terzaghi.
• Generally recognized as the father of modern soil
mechanics and geotechnical engineering.
• He started modern soil mechanics with his
theories of consolidation, lateral earth pressures,
bearing capacity, and stability.
• His contribution has spread to almost every topic
in soil mechanics and geotechnical engineering
covered by the text book: Effective stress; Elastic
stress distribution; Consolidation settlement;
Shear strength; in situ testing

17. • The term Soil mechanics was coined by Dr.
Karl Terzaghi in 1925 when his book
Erdbaumechanic on the subject was published
in German.
• According to Terzaghi : ― Soil mechanics is the
application of laws of mechanics and hydraulics
to engineering problems dealing with sediments
and other unconsolidated solid particles
produced by the mechanical and chemical
disintegration of rocks regardless of whether or
not they contain an admixture of organic
constituents.”

18. Karl von Terzaghi Observing the
Experimental Setup

19. • Soil includes widely different materials like
boulders, cobble, gravels, sands, silts, clays.

20. Different types of soils

22. Scope of Geotechnical/soil
engineering
• The soil engineering has very large application in
the construction of various civil engineering works.
• The physical properties of soil mechanics is
particularly helpful in the following problems of civil
engineering.
• Foundation design and construction
• Retaining structures
• Underground structures
• Stability of slopes
• Pavement design
• Design of earth dams

23. Foundation design and
construction
• Foundation is an important elements of all civil
engineering structures.
• Every structure like building, bridge, dam,
highway, tunnel, canal is founded in or on the
surface of the earth.
• Foundations are transmitting the load of the
structure to the soil safely.
• The suitability of various types of foundation
spread foundation, pile foundation, deep
foundation etc. depend upon the soil strata,
load and ground water conditions.

25. Retaining structures
• The structure which retains large mass of earth
on its side is called retaining structures.
• Live example :~ A large retaining wall
constructed along the Sabarmati river at river
front in Ahmedabad in an example of retaining
structure.
• The theory of earth pressure given by soil
engineering is required to design such retaining
structures.

27. Underground Structures
• It consists tunnels, pipelines, underground
building are subjected to various forces exerted
by soil mass.
• A knowledge of soil structure interaction is
essential to design properly such structures
subjected to soil loadings.

29. Stability of slopes
• When soil surface of structure is not horizontal
such as in case of highway embankment or
irrigation canal the component of gravity tires to
move the soil downward.
• A complete knowledge of shear strength and
related properties of soil is necessary to design
the slope of embankment (filling) or excavation
(cutting).

31. Pavement design
• A pavement can either be flexible (Bituminous
road) or rigid (Concrete roads). Its performance
depends upon the subsoil on which it rests.
• The thickness of a pavement and its component
parts depend upon certain properties of the
subgrade soil.
• The soil properties such as strength and
stability is very much helpful in constructing
pavements on poor soils by stabilizing them.

33. Design of earth dams
• The construction of an earth dams requires a
very through knowledge of whole of the soil
mechanics.
• It requires the determination of various physical
properties of soil such as density, plasticity,
characteristics, permeability and compaction
characteristics.
• Suitable soil survey of nearby area is also
necessary since huge soil mass is involved in its
construction.
• storage huge volume of water and its failure may
cause wide spread disaster. Therefore extreme
care is taken in its design and construction.

35. Limitation of Geotechnical/soil
engineering
• The solution of the theory of elasticity can not
be applied directly as soil does not possess a
linear stress-strain relationship.
• As the soil at every location is different, the
results and experience from one project can not
be directly applied to other project.
• The strength and the behavior of soils depend
upon pressure, drainage, climate condition and
many other factors.
• The properties of soil like density, pressure,
shear strength, bearing capacity, etc. changes
with the depth of soil.

36. Limitation of Geotechnical/soil
engineering
• The soil is a three phase system consisting of
solids, water and air. The behavior of a soil
depends upon the relative proportion of three
phases.
• The soils are very sensitive to disturbance.
Thus, the results of tests conducted on soil
samples should be interpreted carefully.

37. Fundamental uses of soil
• In civil engineering, soil has two fundamental uses
• 1) As a construction material :
• Highway embankment
• Railway embankment
• Earthen Dam
• Filling in low lying areas.
• 2) As a Foundation :
• Building
• Bridge
• Highway
• Tunnel, Canal, Dam..