A cofferdam is a temporary structure used to keep water or soil out of an excavation for construction. It must be watertight but does not require absolute water tightness, and various materials like earth, timber, steel, and concrete can be used depending on factors such as depth and soil condition. Different types of cofferdams include dikes, single wall, double wall, cellular, rock-filled crib, and concrete, each having unique construction methods and applications.

1. COFFERDAM
PRESENTED BY
JIAD
CIVIL - S5

2. COFFERDAMS
“A cofferdam is a temporary
structure designed to keep water
and/or soil out of the excavation in
which a bridge pier or other
structure is built”.

3. REQUIREMENTS
 Cofferdam should be reasonably watertight.
 Absolute water tightness is not desired in a cofferdam.
 Designed in maximum water level.
 Ground water or water lying above ground level should be
excluded.
 Materials – earth , timber , steel & concrete.
 Constructed at site of work.
 Depend- depth , soil condition , difference in water level,
availability of materials.

4. USES
• Pile driving operation.
• Place grillage & raft foundation.
• Construct new structures.
• Enclose space for removal.
• Constructing without disturbances.

5. FACTORS FOR CHOICE OF
TYPE OF COFFERDAMS
Area to be protected by a cofferdam.
Depth of water to be dealt.
Possibility of over topping.
Nature of velocity of flow.
Availability of materials at site of work.
Easy transportation.

6. TYPES OF COFFERDAMS
 DIKES
 SINGLE WALL COFFRDAM
 DOBLE WALL COFFERDAMS
 CELLULAR COFFERDAMS
 ROCK-FILLED CRIB COFFERDAMS
 CONCRETE COFFERDAMS

7. DIKES
Embankment of some materials.
• EARTH
• ROCK
• SAND-BAGS

8. EARTH DIKES
• Shallow depth of water 1200 - 1500 mm.
• Low velocity of flow
• Free board-1m.
• Suitable side slope.
• Top width of bank.
• Material-mixture of clay &sand.
• Puddle – best material .
• Rip rap – protected against wind & wave actions.

9. • Piece of rock wt. 70 – 700 N.
• After all, construction work of foundation is started.
• Not used in over topping situation.

10. ROCK DIKES
• Depth about 3 m.
• Availability of rock.
• Not impervious.
• Impervious layers of earth are laid on side.
• Voids are filled by earth.
• Sometimes, core wall or steel sheet pile are used.
• Core wall – clay or concrete.
• Prevent over topping.

12. SAND – BAG DIKES
• Mixture of sand & clay in a bag.
 PRECAUTIONS
• Use empty cement bags.
• Voids of sand bag may exceed – 40%.
• Small depth.
• Joints filled with puddle.

13. SINGLE WALL COFFERDAM
• Preferred small area.
• Guide piles, wales , struts – wood.
• Sheet piles are of wood or steel.
• Wooden piles – depth about 10 m.
• More depth - steel piles( 25 m ).

14.  CONSRUCTION
o Soft material - removed.
o Guide piles are driven – 3m.
o Sheet piles are driven with
guide frame.
o Struts & Wales (strength).
o Water pumped out .

15. DOUBLE WALL COFFERDAMS
• In large area.
• Ohio river type & wood or steel sheeting cofferdam.

16. OHIO RIVER TYPE COFFERDAM
• Ohio river in USA.
• Used in hard & soft bed (no erosion).
• Unsuitable in deep water & swift flow.
Construction
• Wales fixed at 1.50m vertically.
• Wale joints, double vertical planks are provided.
• Tie rods threaded & cross braces fixed.
• Fixes sheet piles.
• Berms (inside & outside)
• Removing safely.

17.  WOOD OR STEEL SHEETING
COFFERDAMS
• Depth ( 6-10 m)
• For small & ordinary type
• No possibility of driven of guide piles steel (depth) sheet
piles are used.
• Tie rods connects guide piles.

18. oConstruction
•Driving of guide piles ( 2-3 m) .
•Wales fixed guide piles.
•Driven sheet piles.
•Space filled by puddles.
•Berms provided for safe.

19. CELLULAR COFFERDAM
• Large areas.
• Steel sheet piles.
• Diaphragm cells & Circular cells.

20. • Radius of arcs are equal to distance b/w cross walls.
• Filling height equal (avoid distortion)
Cellular cofferdam – diaphragm cells.

21. Cellular cofferdam-circular cells.
• Radius of arc 2500 mm.
• 30-45 angle .

22.  Advantages
Fast construction work of cells.
Self-supporting unit.
Less quantity of steel per running length (circular cells).
Little false work is required.

23. ROCK FILLED CRIB
COFFERDAM
• Crib is a box / a Cell open at bottom(timber).
• Rock / gravel / earth (overturning & sliding).
• Depth 10-20 m.
• Limited space.
• Cheap material (timber).
• Swift water flow.

24. Construction
1. Made as long for safe handling , wide for structural stability (depth
& current of flow).
2. Bottom on land.
3. Floated & placed in position.
4. Space filled by rock , earth , gravel.
5. Providing sheet piles.
6. Suitable earth filling.
7. Pumping.

25. CONCRETE COFFERDAM
• Frame work of precast R.C.C. piles & sheets.
• Driven as steel sheet piles.
• Disadvantage (COSTLY).
• Avoid vibration (pile foundation).

26. PREVENTION OF
LEAKAGE IN COFFERDAM
Leakage through sheet piling & under flow.
 Fissures / cracks of rock – Pumping cement grout by pipes
(100mm dia ).
Clay , sand , ashes etc. – dumped around cofferdam.
Single wall cofferdam – Placing V- shaped wooden on outside
& Filling puddles.
Leakage in sheet piling – box(sawdust & ashes) hold near
joints , leads to sealing.

27. Interlocks of steel sheet piles – grease.
Double wall cofferdam –
• Driving piles through filling.
• Filling the holes with quick swelling material.
• Forcing clay cylinders for better compactness.

28. ADVANTAGES OF
COFFERDAM
 Poor environment.
 Safe environment.
 Design responsibility.
 Easy work.
 Re-usability of materials.

29. PUDDLE FOR COFFERDAM
o Clay & sand / clay & gravel.
o Clay - cohesive & impermeable.
 Test for cohesive – 40 mm dia 250 mm length cylinder
water(sufficient) .Suspended from one end(wet) ,not break-cohesion.
 Test for impermeability – Plastic mass spread ,water stored above .
Water held for some time –impermeable.
o Layers of 80 mm , well rammed (water should added).

30. FACTORS AFFECTING
DESIGN OF A COFFERDAM
Hydrostatic head of water
Dimensions of area.
Sub-soil condition.
Fluctuations of outside water level.
Possibility of erosion.
Floating logs.
Presence of ice.

31. CONCLUSION
Purely theoretically cofferdam will fail reasonably.
More than theory practical knowledge & experience are
necessary for good construction of cofferdams.

32. ……THANK YOU