Bridge foundation

INTRODUCTION
Foundation is to provided to transmit the
load from the piers or abutments and wings to
and evenly distribute the load on the strata.
It is to be provided sufficiently deep so that
it is not affected by the scour caused by the
flow in river and does not undermined.

TYPES OF BRIDGE FOUNDATION
The choice of bridge foundation depends upon
the importance of bridge, size, nature of soil and
sub-soil in the bed and velocity of water flow.
foundations are grouped under
 Shallow Foundation
 Open Foundation
 Block Foundation
 Deep Foundation
 Pile Foundation
 Well Foundation

OPEN FOUNDATION
Pipe and box culvert can be laid after removing
about 0.30D to 0.50D of top soil in bed and
replacing it with well rammed moorum or laying a
lean concrete bedding after the base is leveled and
well consolidated by ramming or rolling.

OPEN FOUNDATION
Open Foundation in minor bridges will be in
the footing form.

OPEN FOUNDATION
In designing the open foundation, the
maximum pressure at base of foundation is limited
to the values given in the table.

PILE FOUNDATION
Use of pile foundation has till recently not been
a popular choice for bridges in India.
For road bridges, this had been used mostly as
timber pile for temporary bridges and where
subjected to lighter loads.
RCC piles both pre-cast and cast-in-situ as
well as larger diameter bored pipes below bed level
are becoming popular.
A minimum diameter of 1200mm for river
bridge and 750mm for the others is preferred.

PILE FOUNDATION
Use of piles for bridge in India
 Cheap and quick in construction
 Timber piles have been used in railways and
roadways, particularly in the North-Eastern part in
case of temporary bridge.
 In the North-Eastern part of India, many of the rivers
there are of shifting nature and there is always
danger of bridges being out flanked by the rivers
when the river shifts its course.
 The recent development indicate that the pile
foundation can be used quite economically,
particularly, where the foundation have to be built
very deep or taken through deep layers of soil
subjected to a minimum of scour.

WELL FOUNDATION
Well foundation are constructed on dry ground
in suitable form and then sunk into the ground to
the desired level by grabbing the soil through
dredge holes provided, surrounded by the solid
masonry.

WELL FOUNDATION
Components of Well Foundation
 Well Curb:
The structure of well at the bottom is
tapered to end in a steel ‘cutting edge’ which
facilitates cutting through soil for sinking of well.
This tapering portion being thin, it has to be
strengthened suitably to take up the heavy loading.
This portion is called “Well Curb”.
 Steining:
The structure in the form of well
surrounding the dredge holes, is known as
‘steining’.

WELL FOUNDATION
Bottom Plug:
The concrete placed at the bottom to form
the base of foundation for distributing the load to soil
below, is known as “Bottom Plug”.
 Top Plug:
The concrete placed at the top, at finishing
level, to transmit the load of structure to the to the
well steining, is known as “Top Plug”.

WELL FOUNDATION
Advantages
 This provides a solid and massive foundation for
heavy loads and high horizontal thrust transmitted by
the moving loads.
 This has a larger cross sectional area and hence the
total foundation bearing capacity is much larger than
piles.
 Wells can be taken trough soil having boulders, logs
of wood and such type of obstruction, without causing
damage to the structure.

WELL FOUNDATION
 The masonry in the steining of well is built in dry
condition and hence quality of masonry or concrete
can be assured.
 The well provide good grip when taken sufficiently
deep and hence most suited for river beds subjected
to heavy scour.
 Hence, the choice is mostly in favour of well
foundation where large spans requiring deep
foundations have to be provided.

BLOCK FOUNDATION
 is a form of shallow foundation
 used for smaller bridges in locations where there
is a good founding strata at shallow depth
 but is overlain by very soft layer of soil and high
water table making open excavation difficult due
to small quantum of work.

SITE SELECTION
Ideal characteristics of bridge site
1. Suitable, un-yielding, non-erodable material for
foundation should be present at short depth for
piers or abutments.
2. The bearing strata should be free from the
tendency to slip/slide/sink under load.
3. The stream at bridge site should be well defined,
as narrow as possible.
4. There should be straight reach of stream at
bridge site.

SITE SELECTION
5. The site should have firm, permanent, straight
and high banks.
6. The flow of water at in stream at bridge should be
steady.
7. It should be feasible to have straight approach
road and square alignment.
8. There should be minimum obstruction of water
way so as to have minimum afflux.
9. There should be no need for costly river training
works in vicinity of bridge site.

SITE SELECTION
10. At bridge site it should be possible to provide
secure and economical approaches.
11. In order to have minimum foundation cost the
bridge site should be such that no excessive
work is carried out inside water.
12. In order to achieve economy, there should be
easy availability of labour, transport facilities,
construction material in the vicinity of bridge site.

SITE SELECTION
13. There should be no confluence of large
tributaries in the vicinity of bridge site.
14. In case of curved alignment, the bridge
should not be on the curve but preferably on
the tangent, since otherwise there is more
probability of accidents.
15. The bridge site should be such that adequate
vertical height and water way is available
underneath the bridge.

Bridge foundation

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