This document discusses cofferdams, which are temporary structures built to remove water from an area and allow construction work under dry conditions. It outlines the requirements, necessity, uses, factors affecting selection, and common types of cofferdams. The types discussed include earthen, rock-filled, sand bag, single wall, double wall, cellular, crib, concrete, and suspended cofferdams. Forces acting on cofferdams and the economical height are also summarized.

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3. PATEL PRANAV R. (106560306127)
PATEL SANJAY B. (106560306089)
NAYI VISHAL A. (106560306101)
BHAGAT HARSH G. (116560306098)
PATEL DENISH D. (096560306128)
PATEL VISHAL P. (116560306027)
DESAI MOHIT D. (096560306050)

4. Contents :-
 Introduction
 Requirement of a cofferdam
 Necessity of cofferdam
 Use of cofferdam
 Factor affecting selection of cofferdam
 Types of cofferdam
 Forces acting on cofferdam
 Economical height of cofferdam

5. Introduction :-
 A cofferdam is a temporary
structure which is built in a
river, lake etc. to remove
water from an area and
make it possible to carry on
the construction work
under reasonably dry
conditions.
 Cofferdams are usually
required for project such as
dams and construction of
piers and abutment.

6. Requirement of a cofferdam :-
• The cofferdam should be reasonably watertight.
• It should be generally constructed at site of work.
• The design and layout of a cofferdam should be such that
the total cost of construction, maintenance and pumping is
minimum.
• It should be stable against bursting, overturning and
sliding, under the floods and waves.
• The water to be excluded by a coffer dam may be either
ground water of water lying above ground level, it may be
deep or shallow and still or running.
• The materials used in construction of a cofferdam are
earth, timber, steel and concrete.

7. Necessity of cofferdam :-
 The coffer dams are required in the following situation:
 When it is required to construct a structure in the river
bad.
 When structure is to be constructed on a sea shore.
 When it is required to construct a structure one a bank of
the lake or inside the lake.
 When deep excavation are carried out in a course grained
soil.
 When excavation is carried out below ground water table.
 During deep excavation, when sides of the trenches are
likely to collapse.

8. Use of cofferdam
 To facilitate pile driving operation
 To place grillage and raft foundation
 To construct foundations for piers and abutments of
bridge, dams, locks, etc.;
 To enclose a space for the removal of sunken vessels
 To provide a working platform for the foundation of
building when water is met with; and
 To provide space for carrying out the foundation work
without disturbing or damaging the adjoining
structure such as buildings, pipelines, sewers, etc.

9. Factor affecting selection of cofferdam
 The selection of a type of cofferdam depends upon the
following factors:
 The size of area which is protect by cofferdam
 Depth of water
 Flow of water
 velocity of flowing water.
 The nature of bed on which the cofferdam is to rest.
 Availability of materials at the site
 The Possibility of overtopping by floods, tides etc.
 Transportation facility of machine equipment and
materials

10. Types of cofferdam :-
 Earthen cofferdam
 Rock-filled cofferdams
 Sand bags cofferdam
 Single wall cofferdams
 Double wall cofferdams
 Cellular cofferdam
 Crib cofferdam
 Concrete cofferdam
 Suspended or floating cofferdam

11. Earthen cofferdam :-
 This is the simplest form of cofferdam. It essentially consist
of an earthen embankment built around the area to be
enclosed.
 Suitable for low, 1.2 to 1.5 m and moderate head of water.
 The top of embankment should be 1m above the water level.

12. Rock-filled cofferdams :-
 Suitable for turbulent flow and up to 3m depth of water.
 Stone or rubble is used for the embankment.
 It construction is adopted only the stone is easily available
in the nearby areas.

13. Sand bags cofferdam :-
• The method of
using laminated
sand bags to
build cofferdam
are easy to
construct, cost-
efficient and
economic
friendly

14. Single wall cofferdams
• This type of
cofferdam is used
in places where the
area to be enclosed
is very small and
the depth of water
is more, say 4.5 to 6
m.
• It can be used for
up to 25m depth of
water.

15. Double wall cofferdams :-
 Two-parallel rows of steel
sheet piles driven into the
ground
 Tied together with anchors
and wales, then filled with
soil
 There are two types of this
type of cofferdams:
1. ohio river type wood
sheeting cofferdam
2. Wood or steel sheeting
cofferdam with wales and
tie rods

16. Cellular cofferdams :-
 Circular cells are connected
by diaphragms
 Deep excavations
 Used when the construction
area is very large
 Also used when internal
bracing is impractical
 There are two types of this
type of cofferdams:
1. Circular
2. Diaphragm

17. Crib cofferdam
•In deep water where it is difficult to
penetrate the guide piles or sheet
Piles into the hard bed below ,crib
cofferdam is used.
•In these type of construction ,the
sheet piles are supported by a series of
wooden cribs.

18. Concrete cofferdam
• when construction must take place below the water level, a
cofferdam is built to give works a day work environment.
•sheet piling is driven around the work site, seal concrete is placed
into the bottom to prevent water from seeping in from underneath the
sheet piling, and the water is pumped out.

19. Suspended Cofferdam
•cofferdam which is freely suspended and has a
characteristics of floating.
•it is a box type cofferdam.

20. Forces acting on cofferdam :-
 Self weight of cofferdam
 Water pressure
 Earth pressure from out side soil
 Uplift pressure
 Scouring action
 Ice pressure
 Other action

21. Economical height of cofferdam
• The maximum height of cofferdam for which its
total cost is minimum is known as the most
economic height of cofferdam.
• When cofferdam is constructed in a river. It is
necessary to determine the height that will most
satisfactory. Usually the height of cofferdam is
determined based on the height of the average
normal flood during every year.