CIVIL ENGINEERING FOUNDATION

1. FOUNDATION

2. Function of Foundation
 Reduction of load intensity:- intensity of load should not
exceed the safe bearing capacity of sub-soil.
 Even distribution of load:- it distributes non uniform load
from super structure evenly on sub-soil.
 Provision of level surface:- it provides level & hard surface
over which super structure can be built.
 Lateral Stability:- it provide anchoring support to super
structure, giving stability to building against sliding & overturning.
 Safety against undermining:- provides safety against
undermining & scouring due to borrowing of animals or flood water.
 Protection against soil movement:- safety against
expansion or contraction of sub soil.

3. Requirement of a foundation
 Sustain & transmit all the load coming on foundation
 Minimize differential settlement
 Guard building against damage due to shrinkage &
swelling of soil

4. FOUNDATION
foundation
Shallow
Step
footing
For
column
Simple Stepped grillage
For
walls
Simple Stepped grillage
strap
footing
Combined
footing
Rectangular trapezoidal
Mat
footing
Deep
Pile pier well

5. Shallow Foundation
 According to terzaghi, a foundation is shallow if its
depth is equal to or less its width.

6. Spread Footing
 Spread footing is those which spreads the super-
imposed load of wall or columns over a large area.
 Single footing for wall/column
 Stepped footing for wall/column
 Sloped footing for wall/column
 Grillage foundation

8.  Simple spread footing:- when the wall/column carries
light load & safe bearing capacity of soil is high.
 Stepped footing:- when wall carry heavy load or safe
bearing capacity of soil is less.
 Sloped footing:- the thickness at junction & at base
varies.

9. Grillage Foundation
 It is a special type of isolated footing, generally
provided for heavily loaded steel stanchions, when
bearing capacity of soil is poor.
 The depth of foundation is limited to 1 to 1.5m
 The heavy load is distributed to a large area by means
of layers or tiers of joist
 Grillage foundation are of two types
 Steel grillage foundation
 Timber grillage foundation

10. Steel grillage foundation

11. Timber grillage foundation

12. Combined footing
 Spread footing which supports two column is called
combined footing.
 Combined footing are provided when
 The columns are very near two each other so that their
footings overlap.
 When bearing capacity of soil is less and require more area
under single column
 When end column is near property line and footing cannot be
spread in that direction.
The design of combined footing is done such that centre of
gravity of column loads coincide with the centroid of the
footing area.

13. Rectangular footing Trapezoidal footing

14. Strap Footing
 Strap footing comprises of two or
more footing of individual column,
connected by a beam, called strap.

15. Raft/Mat Foundation
 A raft is a combined footing that covers the entire area beneath a
structure & supports all columns.
 When allowable soil pressure are low or structure loads are
heavy, the use of spread footing covers more than half of the
area.
 They are also used in area where soil mass contains compressible
lenses so that differential settlement is controlled.
 A raft may undergo double settlement without causing harmful
differential settlement. Because of this double settlement of that
permitted for footing is acceptable to raft footing.
 When hard soil is not available within 1.5 to 2.5m depth raft
foundation are adopted.

17. Deep foundation are those in which depth of
foundation is very large compare to its width

18. •Pile is a column support type of foundation which may be cast in situ
or precast.
•Piles may be placed separately or they may be placed in cluster
•Pile foundation is adopted where load of structure is heavy and
distribution is uneven.
•Top soil has poor bearing capacity
•Subsoil water level is high
•If deep strip foundation is attempted, timbering of sides is difficult
to maintain soil of sides
•Structure is situated on the sea shore or river bed, where there is
danger of scouring action.
•Top soil of expansive nature.

19. piles
function
End bearing pile
Friction pile
Screw pile
Compaction
pile
Uplift pile
Batter pile
Sheet pile
material
Cement
concrete pile
Timber pile
Steel pile
Sand pile
Composite
pile

20. End bearing pile Friction pile
 These pile penetrate through
soft soil and their bottom or
tips rest on a hard stratum.
 The soil gives lateral support
and increases load carrying
capacity of pile
 When loose soil extend greater
depth, piles are driven up to such
a depth that frictional resistance
developed at side of piles equals
the load coming on the pile.
 Frictional resistance can be
increased by
 Increasing dia of pile
 By driving pile to greater depth.
 By making surface of pile rough
 By placing pile closely & grouping
it.

21. Screw piles Compaction piles
 It consist of hollow cast-iron
or steel cylinder with one or
more blades
 They are used to compact
loose granular soil in order to
increase their bearing
capacity.
 These piles themselves do not
carry any load

23. Uplift piles
The piles anchor down the
structure subjected to
uplift pressure due to
overturning movements

24. Batter piles
 They are used to resist large
horizontal or inclined forces.
Sheet piles
 They are used as bulk head or
impervious cut off to reduce
seepage & uplift

27. Cement concrete piles
Precast concrete piles
 Manufactured in factories
 Square, round or octagonal in shape.
 Having parallel or tapered sides.
 Can bear maximum design load of 80
tones.
 Require place for casting & storage
 More time required to set & cure
before installation.
 Large cost incurred in cutting or
adding of extra length.
 Can be driven under water
 Have proper control over composition
& design of pile.
 Any defect in casting of pile can be
repaired.
 High resistance to biological &
chemical actions of ground.
Cast-in-situ concrete piles
 Piles are easy to handle
 Do not require extra
reinforcement to resist stressed
developed due to handling &
driving of pile.
 No wastage of material
 Transportation cost eliminated.
 Difficult to maintain
reinforcement in correct
position.
 Can not be constructed under
water .
 Not possible to have proper
control over the composition &
design.

30. Timber piles
•Prepared from trunk of
trees.
•Circular or square in shape.
•30 to 50cm dia with length
not exceeding 20times top
width.
•Cast iron shoe is provided at
the bottom & steel plate at
top is fixed.
•Group of piles are provided
with concrete caps to have
common platform.
•Have small bearing capacity.
•Impossible to drive piles in
hard ground.
•Temporary until treated.

31. Steel Piles
 H-piles:- suitable for trestle type of pier in which pile extend above ground level. & also
act as column.
 Used as long piles
 High bearing capacity
 Can be easily driven in soil in which it is difficult to drive ordinary pile.
 Box Piles:- rectangular or octagonal in shape filled with concrete.
 Used when not possible to drive H piles.
 Tube Piles:- tube or steel pipes are driven in ground & filled with concrete.
 Piles are easy to handle & drive in ground due to circular section.
 Advantage of steel piles:
 Easily withstand the stresses due to driving .
 Easily lengthened & cutter.
 Bearing capacity is very high
 Can take impact stresses & resist lateral forces.
 Corrosion is the disadvantage in steel piles

33. Sand Piles
 Piles are formed by making holes in ground & filling it
with sand.
 Top is filled with concrete to prevent sand ejecting
upward due to lateral pressure.
 Piles are spaced at 2 to 3m.
 Length of pile is 12 times of dia.
 Easy to construct
 Can be used for any position of water table.
 Not suitable for place where there is danger of scour.
 Earthquake prone.

34. Composite pile
•Composition of bored +
driven pile.
•Composition of two
different material.
•Economical & easy to
construct.
•Suitable where the upper
part of pile is to project
above the water table.

35. Piers
•Consist of cylindrical column of large
diameter to support and transfer
imposed load on it to firm strata
below.
•Transfers load through bearing.
•Shallow in depth than pile
foundation.
•Preferred in location where the top
strata consist of decomposed rocks
overlying a strata of sound rock.
•Pier foundation is of two types
•1.masonry or concrete pier
•2.drilled caisson
•When good bearing strata exists
upto 5m below ground level, brick,
masonry, or concrete foundation pier
is excavated.

36. Box Caisson
•It is opened at top &
closed at bottom.
•Made up of timber,
reinforced concrete or
steel.
•Built on land and then
floated to place requoired.
•Used for shallow depth
where bearing strata is
available.

37. Open Caisson
 It is opened at both the end.
 Made up of timber, reinforced concrete or steel.
 Used for building or bridge foundation
 It is also called as well foundation & this are most
common type of foundation for bridges in India.
 Used on sandy or soft bearing stratum liable to scour
and where no firm bed is available for larger depth
below

39. Excavation of
foundation
Excavation of foundation can be
done either manually or with help
of conventional methods.

40. Timbering of foundation
 When depth of trenches is large or sub soil is loose,
the sides of trenches may cave in. this problem can be
solved using method of timbering.
 Timbering can be done with help of following method
 Stay bracing
 Box sheeting
 Vertical sheeting
 Runner system
 Sheet piling

41. Stay Bracing
•Used for supporting sides or
benches in fairly firm soil when
depth of excavation is 2m.
•It consists of placing vertical
sheets (sheathing/polling boards)
opposite to each other against two
wall of the trench & holding them
in position by one or two rows of
struts.
•Sheet are placed at an interval of 2
to 4 m , extended to full height of
trench.
•Polling board size:- width 200mm
, thickness 40 to 50mm.
•Strut:- (100*100)mm for 2m wide
trench
(200*200)mm for 4m wide trench

42. Box sheeting
•This method is adopted in loose
soil, when depth of excavation is not
more than 4m.
•In this the sheathing are provided
vertical & very close or next to each
other which are further supported
longitudinally by Wales.
•Struts are than provided across the
Wales.
•For very loose soil
•the sheathing are provided
longitudinally & very close or next to
each other which are further
supported by verticalWales.

43. Vertical sheeting Runner system
 This method is used deep
trenches ( up to. 10m depth)
 It is similar to box sheathing ,
excavation is carried out in
stages at end of each stage an
offset is provided
 So that width of trench goes on
decreasing with increase in
depth.
 Each stage is limited to 3m
height and offset vary from 25 to
50cm per stage.
 For each stage separate vertical
sheathing & support by
horizontal wailing & strut is
provided.
 This is used for extremely
loose or soft ground.
 In place of vertical sheeting ,
runner made up of long thick
wooden sheets or plank with
iron shoe at end is provided
 Runner are driven 30cm in
advance of the progress of the
work by hammering.


45. Failure of foundation & remedial measurements
Reasons of failure Due to Remedial
measures
Cause of failure
Unequal settlement
of soil
1) Non uniform
nature of sub-
soil.
2) Unequal load
distribution
3) Eccentric loading
1) Resting of
foundation on
hard ground.
2) Proper design of
base of footing.
3) Limiting pressure
on soil.
4) Avoiding
eccentric loading
May lead to crack in
structure and
rotation of
foundation
Unequal settlement
of masonry unit
Shrinking or
compression of
masonry joints
1) Using mortar of
proper strength.
2) Using thin
mortar joints.
3) Restricting
height of
masonry.
4) Properly watering
the masonry
Crack in super
structure

46. Sub-soil moisture
movement
Cause due to
fluctuation of
water table
Pile foundation Leads to failure of
footing crack in
footing & super
structure
Lateral pressure on
walls
Lateral pressure
coming form pitched
roofs or arches or
winds
Proper design
consideration
Overturning of
foundation or by
generation of tensile
stresses on one side
& compressive on
other side of footing
Lateral movement of
sub-soil
Soft soil liable to
move or slide under
vertical load. Sloping
ground
Sheet piles should be
driven to prevent
lateral movement in
soil.
Excessive settlement
& structure may
collapse
Weathering of soil
due to trees & shrubs
Growing of tree or
shrubs near to
structure
Proper planning Depression of
structure.
Crack in wall or
foundation
Atmospheric action Atmospheric agent
like sun, wind, rain
Filling trenches with
good soil
Providing gentle
Decrease in strength
of structure.