A cofferdam is a temporary structure, which is constructed to remove water from an area of excavation, either ground water or water lying above ground level, and make it possible to carry out the construction work under reasonably dry conditions.

1. Prepared By
Prof. Ashish Makwana
Civil Engg. Dept.
Prof. Ashish Makwana 1

2. PRESENTATION
OUTLINE…
• Definition
• Uses of Cofferdams
• Selection of type of cofferdams
• Type of cofferdams
• Design features of cofferdams
• Prevention of leakage in cofferdams
• Economic height of cofferdams
• Piping in single-wall cofferdams
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3. INTRODUCTION
DEFINITION
• A cofferdam is a temporary structure, which is
constructed to remove water from an area of excavation,
either ground water or water lying above ground level,
and make it possible to carry out the construction work
under reasonably dry conditions.
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4. USES OF COFFERDAMS
• The cofferdams are constructed to facilitate pile driving
operations.
• It is used to place grillage as well as the raft foundations.
• It is constructed to provide working platform for the
foundations of buildings.
• It is used, when the foundations for piers and abutments
of a bridge, dams etc. are to be constructed.
• It is constructed to enclose a space for the removal of
sunken vessels.
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5. SELECTION OF TYPE OF
COFFERDAMS
• The depth of water to be dealt with e.g. the earth fill
cofferdams are suitable for low heads of water in still
or sluggishly moving water.
• The area to be protected by a cofferdam. e.g. single
wall sheet pile cofferdams are suitable for narrow
excavations and restricted site areas and double wall
cofferdams or cellular sheet piling for wide
excavations.
• The materials available at site of work for construction
of cofferdam. e.g. Rock filled timber cribs would be
suitable for a remote site, where heavy timber in log
form is available and the cost of importing and
transporting steel-sheet piling and the necessary plant
to handle and drive it might be high.
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6. • The possibility of overtopping by floods tides,
etc. e.g. Rock filled crib cofferdams are
suitable to give stability to the crib against over
topping.
• The nature of bed on which the cofferdam is to
rest. e.g. A heavy earth filled crib or cellular
cofferdam could not be carried by deep deposits
of soft clay and single wall sheet piling would be
required in these conditions.
• The nature of velocity of flow, i.e. water flowing
with slow current or with swift current. e.g. The
rock filled crib cofferdams are employed, when
the current of water is swift, similarly earth fill
cofferdams are suitable for slow current.
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7. • The chances of bed erosion due to reduction of water
way caused by the construction of a cofferdam. e.g. Ohio
river type or double wall cofferdams are suitable for hard
bed, where there is no problem of erosion.
• The facilities available for the transport of equipment and
materials required for the construction of a cofferdam.
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8. TYPE OF COFFERDAMS
1. Earth fill cofferdams
2. Rock fill cofferdams
3. Timber crib or Rock filled crib cofferdams
4. Sheet pile cofferdams
– Single wall cofferdams
– Double wall cofferdams
– Cellular cofferdams
5. Movable or suspended cofferdams
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9. Earth fill cofferdamsProf. Ashish Makwana 9

10. Rock fill cofferdams
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11. Rock fill cofferdamsProf. Ashish Makwana 11

12. Timber crib or Rock filled crib cofferdamsProf. Ashish Makwana 12

13. Single wall cofferdams
Sheet pile cofferdams
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14. (Double wall cofferdams)
Sheet pile cofferdams
Ohio-river type Cofferdams
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15. (Double wall cofferdams)
Timber or Steel sheeting Cofferdams
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16. Circular type Cellular CofferdamProf. Ashish Makwana 16

17. Diaphragm type Cellular CofferdamProf. Ashish Makwana 17

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26. DESIGN FEATURES OF COFFERDAMS
(i) Hydrostatic head of water
(ii) Dimensions of the area to be covered by the cofferdam
(iii) Subsoil conditions
(iv) Fluctuations of outside water level
(v) Possibility of erosion
(vi) Presence of ice
(vii) Floating logs, etc.
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27. THANK YOU
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