This document discusses different types of well foundations used in India for major bridges. Well foundations are commonly used in India and have been for centuries, with a notable example being the foundations of the Taj Mahal. The document outlines different shapes of well foundations, including circular, double D, twin circular, double octagonal, and rectangular wells. It also discusses open caisson foundations, box caisson foundations, and pneumatic caisson foundations, providing details on their construction methods and advantages and disadvantages.

2.  Well foundation is the most commonly adopted
foundation for major bridges in India. Since then many
major bridges across wide rivers have been founded on
wells.
 Well foundation is preferable to pile foundation when
foundation has to resist large lateral forces.

3.  Well foundations have
been used in India for
centuries.
 The famous Taj Mahal at
Agra stands on well
foundation.

4.  To know the different types and shapes of well
foundations.
 To know their relative merits and demerits.

5.  Wells have different shapes and accordingly
they are named as:-
1. Circular well,
2. Double D well,
3. Twin circular well,
4. Double octagonal well,
5. Rectangular well.

6.  .

7. Well
Open caisson
or well
Box Caisson
Pneumatic
Caisson

8.  Open caisson are hollow chambers;
 The top and bottom of the caisson is open during construction. It
may have any shape in plan.
 The caisson is sunk into place by removing the soil from the inside
of the shaft until the bearing stratum is reached.

11.  The advantages of open caissons are their feasibility to be sunk to
great depths.
 Their construction cost is relatively low.

12.  The disadvantages of the open caissons are that the bottom of the
caisson cannot be thoroughly cleaned and inspected.
 The concrete seal placed in water is not satisfactory and soil near
the cutting edge may require hand excavation by diver.
 If obstruction like boulders or logs are encountered the construction
gets slowed down.

13. It has a working chamber at the bottom of the caisson which is kept
dry by forcing out water under pressure, thus permitting excavation
under dry conditions.

14.  As there is an access to the bottom of the caisson, obstruction can
be easily removed.
 The soil can be inspected and the soil samples can be ,if required.
 Soil bearing capacity can be determined by conducting in-situ tests
in the working chamber.
 Excavation and pouring of concrete is one in the dry.
 There is no settlement of the adjoining structures as the water table
is not lowered.

15.  Pneumatic caissons are highly expensive Pneumatic caisson should
be used only when open caissons are not feasible.
 The penetration depth of below water table limited to 30 to 40 m.
 There is a lot inconvenience caused to the workmen while working
under high pressure, the workers may develop caisson disease.
 In pneumatic caisson, large amount of manual work is required
which increases the cost.

16.  Floating caissons are open at the top but closed at the bottom.
 These caissons are constructed on land and then transported to the
site ,and floated to the place where these are to be finally installed.
 These are sunk at that place by filling them with sand, ballast, water
or concrete to a levelled bearing surface.

18.  .

19.  The installation of the floating caisson quick and convenient.
 As the floating caisson are prefabricated or precast, the quality of
construction is good.
 Floating caisson are less expensive than open caissons.
 Floating caisson can be transported by floating at a relatively low
cost.

20.  The load carrying capacity of a floating caisson is much lower than
that of equivalent open caisson.
 The foundation bed has to be levelled before installation.
 The base of the floating caisson is to be protected against scour
action.

21.  M.N Som. , S.C Das , Theory and practice of foundation design ,
Ashok.k.Ghosh,New Delhi,2006.
 P.C.Varghese,Foundation Engineering,
Ashok.k.Ghosh,New Delhi,2005.
 Bowles, J.E. ,Foundation Analysis And Design(International
Student Edition) ,Mc-Greww hill,Singapore,1988.
 Saha G.P. “Analysis and Design of Varanasi Bridge
Well Foundations – A Conceptual Approach” Journal
of Indian Roads Congress Vol. 54-2. Paper
presented in the Annual Session of IRC in November
1993.