This document provides an overview of foundation engineering. It begins with definitions of foundations and footings, noting that foundations transmit loads from the superstructure to the underlying soil. It then discusses different types of shallow foundations, including isolated, strip, combined, and raft foundations. Deep foundations like pile foundations are also introduced. The document covers footing design considerations such as depth, spacing, and stability. It explains bearing capacity and failure modes in soil. In summary, the document provides a high-level introduction to foundation types, design requirements, and bearing capacity fundamentals.

1. Lecture
1
INTERNATIONAL UNIVERSITY
FOR SCIENCE & TECHNOLOGY
‫وا‬ ‫م‬ ‫ا‬ ‫و‬ ‫ا‬ ‫ا‬
Dr. Abdulmannan Orabi
Civil Engineering and Environmental
Department
303421: Foundation Engineering
Introduction & Types of Foundation

2. 2
References
ACI 318M-14 Building Code Requirements for Structural
Concrete ( ACI 318M -14) and Commentary, American
Concrete Institute, ISBN 978-0-87031-283-0.
Bowles , J.,E.,(1996) “Foundation Analysis and Design” -5th
ed. McGraw-Hill, ISBN 0-07-912247-7.
Das, B., M. (2012), “ Principles of Foundation Engineering ”
Eighth Edition, CENGAGE Learning,
ISBN-13: 978-1-305-08155-0.
Syrian Arab Code for Construction 2012
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3. A structure essentially consists of two
parts, namely the super structure which is
above the plinth level and the substructure
which is below the plinth level.
Definition of Foundations
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4. Definition of Foundations
The substructure or foundation
is the part of a structures that is usually placed
below the surface of the ground to transmit the
load from the superstructure to the underlying
soil or rock.
Generally about 30% of the total construction
cost is spent on the foundation.
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5. Definition of Foundations
Footings are those parts of the foundation which
resting directly on the soil, support specific
portion of building and distributed building
loads directly to the soil.
The most efficient footing and foundation system is
that transmit building loads mostly to the soil
without exceeding the bearing capacity of the
soil.
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6. Definition of Foundations
All soil compress noticeably when loaded and
cause the supported structure to settle.
If soil of sufficient bearing capacity lies
immediately below the structure then the load
can be spread by footings as shown below.
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7. Loads must be carried by a foundation system
would include the dead load of the building
and live loads of it occupants and contents.
Foundation system must resist lateral loads
from both ground pressure and wind, and
provide anchorage for the building
superstructure against uplift and racking force.
Requirements for Foundations
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8. Requirements for Foundations
The most critical factor in determine the foundation
system of building is the type and bearing capacity
of the soil to which the building loads are
distributed. ( Adequate safety)
Small settlements ( Total and differential settlement)
Construction problems ( stability of excavation
bottom heave ground water problems)
Economical requirement
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9. Footing depth and spacing
1. The forts line
2. Zones of high volume change due to moisture
fluctuations.
3. Top soil or organic material
4. Peat and muck
5. Unconsolidated material such as abandoned
garbage dumps and similar filled in areas.
Footings should be carried below:
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10. Footing depth and spacing
Foundations should be placed at an
acceptable level with respect to adjacent
foundations.
Foundations should be placed sufficiently
away from the edge of a sloping ground
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11. Footing depth and spacing
When footings are to be placed adjacent to an existing
structure, as indicated in figure (1) the line from the
base of the new footing to the bottom edge of the
existing footing should be or less with the
horizontal plane.
From this requirement it follows that the distance m
of figure (1) should be greater than the difference in
elevation of the two footings, Z.
45
Recommendations for footing adjacent to existing structures
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12. Footing depth and spacing
Figure (1)
m
Z
45
New footing
Existing footing
The difference in levels between adjacent
foundations should not cause undesirable
overlapping between stresses.
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13. Excavation may cause settlement to old
foundation due to lateral bulging in the
excavation and/or shear failure due to
reduction in overburden stress in the
surrounding of old foundation
Footing depth and spacing
Recommendations for footing adjacent to existing structures
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14. Footing depth and spacing
New footing
Existing footing
Ground surface
Excavation line
Soil bulges from loss
of lateral support
Figure (2)
S
Recommendations for footing adjacent to existing structures
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15. Footing depth and spacing
Figure (2) indicates that if the new footing is
lower than the existing footing there is a
possibility that the soil may flow laterally from
beneath the existing footing.
This may increase the amount of excavation.
Somewhat but, more importantly may result in
settlement cracks in the existing building.
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16. The two main types of foundation are :
Shallow foundation (spread, combined,
and mat foundations) and
Deep foundation: Pile foundation
Pier foundation
Types of Foundations
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17. Sallow Foundation
Shallow foundation
Foundation soil
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18. Shallow Foundations
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19. Types of Footing
Combined Footing
Combined
Footing
Isolated footing
Strip footing / or
continuous
Strap footing or
cantilever
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20. Isolated Footing
Df
H
Rectangular or Square footing with constant
thickness
N
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21. Isolated Footing
2 5 9. 70
1 87 .0 2
6 8 .1 2
1 2 2 .9 9
Df
H
N
B or L
H
N
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22. Strip Footing
q (kN/m)
2 5 9. 80
56 .1 4
Bearing Wall
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23. Combined Footing
3 82 .9 1
2 4 2. 66
N1
N2
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24. Combined Footing
Rectangular NA < NB
Property line
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25. Combined Footing
Interior
column
Exterior
column
N1
N2
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26. Raft ( Mat ) Foundation
Strip footing in both directions
Strip footing in both direction may be sufficient to
spread the load and reduce soil pressure to acceptable
levels. If not a raft foundation may be give suitable
bearing pressure.
Raft foundation
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27. Deep Foundations
Pile Foundations
If a soil pressure has insufficient
bearing capacity then it is necessary
to use deep foundation, such as pile,
to transmit the load to deeper, firmer
strata.
bed rock
weak soil
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28. Deep Foundations
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29. Deep Foundations
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30. Retaining Walls
Road
Train
retaining
wall
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31. Sheet Piles
Sheet piles
ship
warehouse
sheet pile
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32. Sheet Piles
Sheet piles
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33. Bearing Pressure Under Footings
Actual pressure is not uniform due to:
1) Footing flexibility
2) Depth of footing below ground surface
3) Type of soil
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34. Soil Pressure Distribution
For a concentrically loaded pad footing the
bearing pressure distribution for a cohesive soil
is the pressure are higher near the edge because
the load produces a shear resistance a round the
perimeter which adds to the upward pressure.
Footing
N
Soil pressure
distribution in
cohesive soil.
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35. Soil Pressure Distribution
For cohesionless soil the pressure are higher at
the center because the individual grains of soil
at the perimeter can shift very slightly outwards
to where the soil stresses are less. N
Footing
Soil pressure distribution
in cohesionless soil.
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36. Soil Pressure Distribution
For design purpose, provided the load is
symmetrical with respect to the bearing area, it is
usual to disregard these variations and assume an
uniform bearing pressure.
N
Axially Loaded Footings: Assume uniform pressure
q, bearing pressure
36

37. Stability
Foundation and retaining walls must be designed
to resist both overturning and sliding.
Overturning : To prevent overturning the
restoring moment due to the vertical load must be
greater than the overturning moment, thus
× > M N
M
a
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38. Stability
Sliding : To prevent the footing from sliding the
resisting of the footing on the soil must exceed
the applied horizontal load, thus
N
+ − >
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39. Stability
+ − >
Where:
is the friction resistance under the base
= +
is the friction angle between concrete and soil
is the passive resistance due to horizontal movement
is the active resistance due to horizontal movement
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40. Bearing capacity of soil
Bearing capacity of soil :
It is defined as the maximum load per unit
area which the soil will resist safely without
displacement
The bearing capacity of the soil can be found
by loading the soil, noting the settlement and
by dividing the maximum load by the area on
which the load is applied.
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41. Main components of a structure including soil
Foundation soil is that
portion of ground
which is subjected to
additional stresses when
foundation and
superstructure are
constructed on the ground.
Super Structure
Foundation
Foundation Soil
Ground Level
Bearing capacity of soil
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42. The maximum load is obtained from the
graph between the settlement and load.
Ultimate Bearing Capacity ( ) it is the
maximum pressure that a foundation soil can
withstand without undergoing shear failure
Ultimate Bearing capacity of soil
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43. Allowable Bearing Pressure ( ) :
It is the maximum pressure the
foundation soil is subjected to considering
both shear failure and settlement.
Ultimate Bearing capacity of soil
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44. Bearing capacity, kPa
Settlement,mm
Ultimate Bearing
Capacity
Safe Bearing
Capacity
Allowable Bearing Capacity
Ultimate & Allowable Bearing capacity
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45. Artificial methods to improve bearing
capacity of soil
By increasing the depth of foundation.
By draining the sub-soil water.
By compacting the soil.
By confining the soil mass.
By cement grouting.
By injecting chemicals like silicates etc.
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46. Failure of medium dense sand ( After photo Dr. Abdulmannan Orabi , 1990)
Bearing Capacity
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47. Modes of shear failure
Depending on the stiffness of foundation
soil and depth of foundation, the
following are the modes of shear failure
experienced by the foundation soil.
1. General shear failure
2. Local shear failure
3. Punching shear failure
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48. General Shear Failure
This type of failure is seen in dense
and stiff soil
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49. Local Shear Failure
This type of failure is seen in relatively
loose and soft soil.
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50. Punching Shear Failure
This type of failure is seen in loose and soft soil
and at deeper elevations. The failure surface in
soil will not extend to the ground surface.
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51. Terzaghi’s Bearing Capacity
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52. General Equation
Hansen’s equation
Df
V
η
+β
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