this ppt is presented by my friend JIAD this is very helpful for you by ubaid pattambi

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