introduction of shallow foundation, types shallow foundation depth and factor affecting it vedio link https://youtu.be/X-EwQTkcwjQ

1. SUBJECT
FOUNDATION ENGINEERING
TOPIC
DEFINITION OF SHALLOW FOUNDATION.
TYPES OF SHALLOW FOUNDATIONS.
DEPTH AND FACTOR AFFECTING IT.
PREPARED
BY
ER. SANJEEV SINGH
SNJV432@GMAIL.COM

2. CONTENT
 Definition of shallow foundation.
 Types of shallow foundations.
 Depth and factor affecting it.

3. SHALLOW FOUNDATION
 A shallow foundation, according to Terzaghi, is one whose width is
greater than its depth ( i.e, 𝐷𝑓/B ≤ 1).
 Shallow foundation are located just below the lower part of the wall or a
column which they support.
 Footing are structural member, made of brick work, masonry or
concrete, that are used to transmit the load of the wall or column such
the load distributed over a large area.

4. TYPES OF SHALLOW
FOUNDATIONS
 Strip Foundation
 Spread or Isolated Footing
 Combined Foundation
 Strap or cantilever foundation
 Mat or Raft Foundation

5. STRIP FOUNDATION
 The foundation whose length is considerably greater than its
width is called strip or continuous foundation.

6. SPREAD OR ISOLATED
FOOTING
 A spread footing is provided to support an individual column.
 A spread footing is circular, square or rectangular slab of
uniform thickness.
 Sometime it is stepped or haunched to spread the load over a
large area.

7. COMBINED FOUNDATION
 A combined footing supports two columns.
 It is used when the two columns are so close to each other
that their individual would overlap.
 Combined footing may be rectangular or trapezoidal in plan.

8. STRAP OR CANTILEVER
FOUNDATION
 A strap footing consists of two isolated footings connected with a
structural strap.
 The strap connects the two footing such that they behave as one unit.
 The strap act as a connecting beam and does not take any soil reaction.
 The strap is designed as a rigid beam.
 A strap footing is more economical than a combined footing when the
allowable soil pressure is relatively high and the distance between the
columns is large.

9. MAT OR RAFT
FOUNDATION
 A mat or raft foundation is a large slab supporting a number
of columns and wall under the entire structure or a large part
of the structural.
 A mat is required when the allowable soil pressure is low or
where the columns and walls are so close that individual
footing would overlap or nearly touch each other.
 Mat foundation are useful in reducing the differential
settlement on non-homogeneous soil.
 Where there is a large variation in the loads on individual
columns.

10. DEPTH AND FACTOR
AFFECTING IT
 Depth of top soil.
 Frost depth.
 Zone of soil volume change.
 Water level.
 Scour depth.
 Underground defects.
 Root holes.
 Minimum depth.

11. DEPTH OF TOP SOIL
 The footing should be located below the top soil consisting of
organic matters which is eventually decompose.
 The top soil should be removed over an area slightly larger
than the footing.

12. FROST DEPTH
 The footing should be carried below the depth of frost penetration.
 If the footing is located at insufficient depth, it would be subjected to the frost
damage due to formation of ice lenses and consequent frost heave.
 During summer, thawing occurs from the top downwards and the melted water is
entrapped.
 As the soil water freezes and melts, the footing is lifted during cold weather and it
settles during warm weather.
 The shear strength of the soil is also decreased during warm weather due to an
increase in water content.
 To prevent frost damage, the footings should be placed below the frost depth,
which may be 1 m or more in cold climate.

13. ZONE OF SOIL VOLUME
CHANGE
 Some soils, especially clays having high plasticity, such as
black cotton soil, undergo excessive volume change. Such as
soil shrinks upon drying and swell upon wetting.
 The volume changes are generally greatest near the ground
surface and decrease with increasing depth.
 Large volume changes beneath a footing may cause alternate
lifting and droping.

14. WATER LEVEL
 The footing should be placed above ground water table as far
as possible.
 The presence of ground water with in the soil immediately
around a footing in undesirable as it reduce the bearing
capacity of the soil and there are difficulties during
construction.

15. SCOUR DEPTH
 The footings located in stream, on water fronts or other
locations where there is a possibility of scouring, should be
placed below the potential scour depth.

16. UNDERGROUND
DEFECTS
 The depth of footings is also affected by the presence of
underground defects, such as faults, caves and mines.
 If there are man made discontinuities, such as sewer lines,
water mains, underground cables, these should be shifted or
the footing relocated.

17. ROOT HOLES
 If there are root holes or cavities caused by burrowing
animals or worms, the footing should be placed below such a
zone of weakened soil.

18. MINIMUM DEPTH
 Is: 1904-1978 specifies that all foundation should extend to a
depth of at least 50 cm below the natural ground surface.
 However, in case of rocks, only top soil should be removed
and the surface should be cleaned.
Where q is the intensity of loading
(𝐷 𝑓)min=
𝑞
γ
(
1−𝑠𝑖𝑛 ’
2
1+𝑠𝑖𝑛 ’
)