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COFFERDAM
PRESENTED BY
JIAD
CIVIL - S5

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��.

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 �C earth , timber , steel & concrete.
? Constructed at site of work.
? Depend- depth , soil condition , difference in water level,
availability of materials.

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

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.

TYPES OF COFFERDAMS
? DIKES
? SINGLE WALL COFFRDAM
? DOBLE WALL COFFERDAMS
? CELLULAR COFFERDAMS
? ROCK-FILLED CRIB COFFERDAMS
? CONCRETE COFFERDAMS

DIKES
Embankment of some materials.
? EARTH
? ROCK
? SAND-BAGS

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 �C best material .
? Rip rap �C protected against wind & wave actions.

? Piece of rock wt. 70 �C 700 N.
? After all, construction work of foundation is started.
? Not used in over topping situation.

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 �C clay or concrete.
? Prevent over topping.

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

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

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

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

?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.

? 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.

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

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

? Radius of arcs are equal to distance b/w cross walls.
? Filling height equal (avoid distortion)
Cellular cofferdam �C diaphragm cells.

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

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

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.

?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.

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

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

?Interlocks of steel sheet piles �C grease.
?Double wall cofferdam �C
? Driving piles through filling.
? Filling the holes with quick swelling material.
? Forcing clay cylinders for better compactness.

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

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

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.

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

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Cofferdam

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