3. What is Foundation/Footing??
It is the lowest part of a structure below
ground level.
Has direct contact with ground.
It provides a base for the super-structure
through the artificial arrangement of
concrete block, piles, raft etc.
It distributes the load of structure over a
large area without stressing the soil
beyond its capacity.
4. Types of Foundations
Foundation
Shallow Deep
Strip Isolated MAT Pile Cassion Cofferdam
Single Combined
5. Single Footing
Used to support single column
One of the most economical types of
footing
Used when columns are spaced at
relatively long distances
Fig: Single footing
6. Construction process of single footing
• Step 01: Excavation of trench
• Step 02: Leveling and dressing
• Step 03: Brick Flat Soling (BFS) placement
• Step 04: Cement Concrete (CC) layer placement
• Step 05: Shuttering/ formwork (must be leak proof) placement
• Step 06: C.C. block (to maintain clear cover) placement
• Step 07: Rebar Placement
• Step 08: Casting of Concrete, C:FA:CA=1:1.5:3/1:2:4, w/c ratio=0.42-0.5
• Step 09: Compaction (to avoid segregation)
• Step10: Removal of shuttering
• Step 11: Curing
• Step 12: Backfilling
8. Step 1:Excavation
• Excavation is the act or
process of digging
• Excavated area depends on
the size & depth of footing.
9. Step 02: Leveling and dressing
• After excavation the soil surface is
levelled.
• The bed is compacted with hand
rammer.
• It is needed to provide a level surface
for setting Brick Flat Soling.
• Sometimes sand & brick chips mix is
used to improve soil condition.
10. Step 03: Brick Flat Soling (BFS) placement
• To construct a hard and
plane surface for rebar
placement and concrete
casting single layer of
bricks is provided.
• Usually 3 inches BSF is
being used
• Frog marks of brick
kept upward direction
11. Step 04: Cement Concrete (CC) layer placement
• 3” cement concrete layer is
provided to make damp
proof layer. (C:FA:CA=
1:3:6)
12. Step 05: Shuttering/ formwork placement
Shuttering is the solid
boundary around the concrete
to keep concrete in shape and
to resist the water flow.
Types :
• Wooden
• Steel
[In our site wooden shuttering
was used]
If the soil condition is good,
polythene is used instead of
shuttering
13. Step 6: C.C. block placement
CC(Cement concrete) blocks are
used to maintain the clear cover
from BFS to reinforcement.
Generally its size is 3 ̋ x 3 ̋ x 3 ̋.
Instead of cc block sometimes
brick bat is also used to maintain
clear cover.
14. Step 07: Rebar Placement
• At first a single frame of horizontal
reinforcements is placed upon the CC
blocks.
• long direction(20mm) reinforcements
are placed at bottom and short
direction(20mm) reinforcements are
placed over it.
• The distance between the bottom of
the footing & reinforcements should
be minimum 3”.
• 3” clear cover is provided
• The reinforcements are tied with G.I
wire.
15.
16. Step 08: Casting of Concrete
• Maintained proper mix
ratio(1:3:5)
• Water should be
pumped out before
casting.
• Casting is started from
center of the footing.
• Setting time of cement
should be maintained.
17. Step 09: Compaction
• Compaction is done to avoid
segregation of the concrete.
• A motor vibrator is used for
compaction
• The entrapped air is
expelled
18. Step 10: Removal of Shuttering
• Approximately after 3 or
4 days the shuttering is
removed.
19. Step 11: Curing
• Uniform temperature should also be
maintained throughout the concrete
depth to avoid thermal shrinkage cracks.
• It directly affects the rate of hydration of
cement
• Curing is provided to maintain an
adequate temperature of concrete in its
early ages.
• Depending on atmospheric condition
curing should be continued at least 21
days.
20. Step 12: Backfilling
• After completing all
process the excavated area
should be filled up with
pure granular soil.
• The filled area should be
compacted to support the
structure.
21. Advantages and Disadvantages of single footing
Advantages:
• Economic
• Shallow single foundation
requires less excavation.
• Size and shape can be
varied depending on site
condition.
Disadvantages:
• Foundation size may
become very large
depending on the loads.
• Weak against uplift force
and lateral forces.
22. Combined Footing
• Combined footing receives load from
more than one column or load-
supporting element.
• Combined footing is either rectangular
or trapezoidal, that supports usually
two or more columns.
23. When we use combined footing?
• Two internal columns are so close that
the two isolated footings overlap.
• Space outside the external column is
limited by property line.
• Bearing capacity of soil is too low.
24. Site Visited (Combined
footing)
• Here is a short clip from our site:
Address
1.Modhubag,
Jheelpara, Dhaka
