2. 2. Pier foundation:
•A Pier foundation consists of a cylindrical column of
large diameter to support and transfer large super-
imposed loads to the firm strata below.
•Piers are holes filled with concrete which act as leg
for foundation
•Piers are used when a heavy structure is to be built
and the firm/hard strata is at reasonable depth
•Construction process comprises sinking vertical
shafts and filling with concrete
4. 2. Pier foundation:………………
Difference between Pile and Pier foundation:
•Difference in methods of construction
•pile foundations transfer the load through friction
and/or bearing but pier foundations transfer the load
only through bearing
•pier foundation is shallower in depth than the pile
foundation
•Pier foundation require less excavation
5. Types of Pier foundation:
(i) Masonry or concrete pier (ii) Drilled caissons
6. (i) Masonry or concrete pier :
•When a good bearing stratum exists upto 5 m below
ground level, brick, masonry or concrete foundation
piers in excavated pits may be used
• The size and spacing of the piers depends upon the
depth of hard bed, nature of overlying soil and super-
imposed loads
7. (i) Drilled caissons :
•The terms drilled caissons, foundation pier or sub-
pier are also termed as cylindrical foundation.
•Drilled caissons are generally drilled with the
mechanical means
8. Drilled caissons may be of three types :
a. concrete caisson with enlarged bottom
b. caisson of steel pipe with concrete filled in the
pipe
c. caisson with concrete and steel core in steel
pipe
10. 3. Well foundation or caissons:
•“Caisson”- french word “caisse”- means box
•Well foundations or caissons are box like structure-
circular or rectangular-which are sunk from the
surface of either land or water to the desired depth
•Adopted for the construction of foundation of bridge ,
pier
•They are much large in diameter than the pier
foundations or drilled caissons
11. 3. Well foundation or caissons:………..
Caisson foundations are used for following
purpose(or in following case):
•To transmit load of the structure to hard bearing
strata lying below deep waters
box
12. 3. Well foundation or caissons:………..
•Caisson foundations are used for major foundation
works, such as for:
bridge piers and abutments in rivers, lakes etc
Wharves, quay walls, docks
Break waters and other structures for shore
protections
Large water front structures such as pump houses,
subjected to heavy vertical and horizontal loads
13. •Well foundations or
caissons are hollow from
inside, which may be filled
with sand and are plugged
at the bottom.
•The load is transferred
though the perimeter wall,
called steining
•Well foundations are not
used for buildings
3. Well foundation or caissons:……
14. 3. Well foundation or caissons:………..
Types of caissons:
a. Box caissons
b. Open caissons or wells or well foundation
c. Monolithic caissons
d. Pneumatic caissons
16. a. Box caissons:
•Box is open at top and closed at the bottom
•May be of RCC, steel or timber
•It is first built on land and then sunk in position
•The cavity is generally filled with sand
•Then the top of caisson is filled with concrete
19. a. Box caissons:………………..
•Box caisson is used in following case:
When the depth of water is not more than 6 to 8m
When the bed material is soft or loose
20. a. Box caissons:………………..
Procedure:
•First of all the base where caisson is to rest is
leveled and consolidated
•If caisson is to rest on group of piles, the head of
piles are leveled such a way that heads of pile lie on
same plain
•The caisson is floated on site of use and slowly sunk
by filling the cavity of box caisson with sand or gravel
22. b. Open caissons or well or well foundation
•Unlike box caisson open caisson is open at both top
and bottom end
•Open caisson is a box of timber, metal or RCC
•Open caissons are known as well and if no. of well
is two it is known as twin well and if more wells than
these are called monolith
•Uneconomical – as heavy timbering is required
•Slow in construction- since greater earthwork
required
23. b. Open caissons or well or well foundation
•Types of open caisson:
i. Single well
ii. Multiple well or monoliths
iii. Cylinder
•Gurucharan pg 113 to 116
24. c. Pneumatic caisson
•Closed at the top and
open (during construction)
at the bottom
•The basic principle is to
isolate the working
chamber from the
surrounding atmosphere
•Working process similar to
the open caisson but in this
caisson the working
chamber is kept air tight
25. c. Pneumatic caisson
•The pressure of air in the shaft is kept higher than
that of the water at the working depth so that the
subsoil water may not enter the working chamber
26. FOUNDATION IN BLACK COTTON SOIL
What is Black cotton soil?
Having properties of shrinkage and swelling due to
moisture movement through them
Swells excessively when wet(wet during rain) and
shrinks when dry
This results cracks in wall and damage lintels,
beams
Have poor bearing capacity
27. Things to be considered while designing footing in
black cotton soil:
•The safe bearing capacity of soil should be properly
determined
•The foundation should be taken at least 50cm lower
than the depth of moisture movement
•If the black cotton soil layer is at the top(1 to 1.5m)
deep, the layer can be completely removed and
foundation can be laid over non-shrinkable and non-
swelling soil
28. Things to be considered while designing footing in
black cotton soil:…………………………
•But if the black cotton soil is at greater depth than
the foundation laid should not be allowed to be in
contact with soil
•In this case the excavation of large width and depth
is dug and insert the layer of sand around and
beneath the footing
•Deeper piles and piers are used
•In case the bearing capacity of soil is low the
foundation trench should be made hard
29. Things to be considered while designing footing in
black cotton soil:……………..
•Better to construct this type of foundation during dry
season
Types of foundation in black cotton soil:
1. Strip or pad foundation
2. Pier foundation
3. Under reamed pile foundation
30. 1. Strip or pad foundation:
•Some special design features as follows are
adopted:
When soil has little swelling pressure
When soil has relatively high swelling pressure
When soil has high swelling pressure
When soil is soft and loose and bearing capacity is
low
31. 1. Strip or pad foundation:…………..
When soil has little swelling pressure:
A layer of of 60cm thick
cohesion less sand is
filled below the
foundation bed and
compacted
Sand is also filled around
the footing
32. 1. Strip or pad foundation:…………..
When soil has relatively high swelling pressure:
By keeping alternate
layers of sand and
ballast/mooram
33. 1. Strip or pad foundation:…………..
When soil has high swelling pressure:
25 to 30 cm thick and wide strips of concrete is laid
over the compacted base of trench
The space or gap between the two strips of concrete
is filled with sand and is equal to the width of bottom
of masonry
Above this strip the foundation bed is laid
Side of foundation laid with sand
34. 1. Strip or pad foundation:…………..
When soil has high swelling pressure:………..
•80mm dia pipe @ spacing
1.5m are placed through
masonry and concrete
reaching sand fill and pipe is
filled with sand
•Plug may placed at the top
of the pipe which can be
removed and placed as per
the work required
35. 1. Strip or pad foundation:…………..
When soil is soft and loose and bearing capacity is
low:
•First of all 30 cm thick layer of
ballast is rammed
•Over it 30cm thick layer of
sand is filled
•Over it lies the concrete bed
of foundation
•Sides of foundation filled with
sand as usual
36. 2. Pier foundation with arches:
•Piers are dug at regular interval and filled with
cement concrete
•Piers rest on hard bearing strata
•Piers at the top are connected through concrete or
masonry arch
•Above masonry arch the walls rest
•Sometimes beams are provided over the arch in
case the arch is constructed of masonry
37. 2. Pier foundation with arches:………
•The arches are constructed high above ground level
•The gap allows the free vertical movement of soil
during swelling and shrinkage operation
38. 3. Under-reamed pile foundation:
•Under reamed piles are bored
cast in situ concrete piles having
bulb shaped enlargement near
base
•A Pile having one bulb is called
single under reamed pile and
having two is double underreamed
pile
•The bearing capacity of the pile is
increased by increasing the
number of bulbs at the base
•The basic principle of under reamed pile is to anchor
the structure at a depth where ground movement are
negligible due to moisture variation or other reasons
39.
40. •Simple tools are
required for construction
of under-reamed piles
like spiral auger, under
reaming tool, and boring
guide
•For speeding up the
construction bore and
under ream for large
diameter and deeper pile
a mechanical rig can be
used
3. Under-reamed pile foundation:…………….
41. •Diameter of the bulb is 2.5
times dia of piles stem or may
vary from 2.5times the dia of
piles
•The c/c distance vertical
spacing between two bulbs(in
case of multi reamed piles) vary
from 1.25 to 1 .5 times the
diameter of bulb
•Length of under reamed piles
varies from 3 to 8m
3. Under-reamed pile foundation:…………….
42. FOUNDATION IN SLOPING SITE
•Generally, it's most economical to place wall footings
at a constant elevation
•If the site or finished grade slopes along the length
of the wall, however, the footing may end up a
considerable distance below finished grade
•This is clearly not economical, as it requires extra
excavation and material
43. Slope the footing with the
site so its depth below the
finished grade is nearly
constant along its length
FOUNDATION IN SLOPING SITE
Step the footing so its
depth below finished grade
is not excessive at any
point along its length
Following options are preferred
44.
45. FOUNDATION IN SLOPING SITE
Sloped Footing Issues
•simple geometry and apparent ease in formwork
construction.
•But create the following construction issues
46. FOUNDATION IN SLOPING SITE
Sloped Footing Issues
•Vertical wall bars above the footing will have different lengths
- increase the quantity of vertical reinforcement
•Horizontal reinforcing bars in the lower portion of the wall will
also have different lengths because they are interrupted by
the sloped footing
•will require trapezoidal formwork- so need modifications to
standard rectangular formwork
•A sloped footing could be unstable, particularly on a very
steep slope and
•Concrete placement and finishing could be difficult, and a stiff
concrete mixture might be required to prevent the concrete
from flowing downhill
47. FOUNDATION IN SLOPING SITE
Considerations For Stepped Footings
For a very long wall- stepped footing more
economical
48. FOUNDATION IN SLOPING SITE
Considerations For Stepped Footings
•It's generally more cost effective to minimize the
number of steps.
•For example, it may be more economical to design
for a 6 ft (1.8 m) change in elevation using three 2 ft
(0.6 m) steps or two 3 ft (0.9 m) steps rather than six
1 ft (0.3 m) steps- This minimizes the number of wall
sections to be detailed and formed
49. CAUSES OF FAILURE OF FOUNDATION AND
THEIR REMEDIAL MEASURES
………………
Bc punmia pg 63
Breakwaters are structures constructed on coasts as part of coastal defense or to protect an anchorage from the effects of both weather and longshore drift.
