PRESENTED BY :-

ANEESH KUMAR CHAUDHARY

ROLL NO :- 1113300016

DEPARTMENT OF CIVIL ENGINEERING

INTRODUCTION

OBJECTIVE

TYPES OF COFFERDAM

METHADOLOGY

FACTOR AFFECTING DESIGN OF COFFERDAM

ADVANTAGES

CONCLUSION

FUTURE ASPECTS

The word "cofferdam" comes from "coffer" meaningbox, in other words a dam in the shape of a box.

A cofferdam is a temporary structure designed tokeep water and/or soil out of the excavation inwhich a bridge pier or other structure is built.

A cofferdam involves the interaction of the structure,soil, and water and the loads imposed include thehydrostatic forces of the water, as well as thedynamic forces due to currents and waves.

The loads imposed on the cofferdam structure byconstruction equipment and operations must beconsidered, both during installation of the cofferdamand during construction of the structure itself.

The main objectives of temporary structure “COFFERDAM” are :-

Pile driving operation.

Place grillage & raft foundation.

Construct new structures.

Enclose space for removal.

Constructing without disturbances

1. Braced: It is formed from a single

wall of sheet piling which

is driven into the ground to form a

“box” around the excavation site.

2. Earth-Type: It is the simplest type of cofferdam. It consists of an

earth bank with a lay core or vertical sheet piling enclosing the

excavation.

3. Timber Crib: Constructed on land and floated intoplace. Lower portion of each cell is matched withcontour of river.

4. Double-Walled Sheet Pile: They are double wallcofferdams comprising two parallel rows of sheetpiles driven into the ground and connected togetherby a system of tie rod sat one or more levels.

5. Cellular: Cellular cofferdams are used only in thosecircumstances where the excavation size precludes theuse of cross-excavation bracing. In this case, thecofferdam must be stable by virtue of its ownresistance to lateral forces.

1 Fixing of alignment for cofferdam : Alignment ofcofferdam shall be fixed on the ground with the help oftotal station as per the relevant drawing.

2 Construction of rock bund : Construction of rock bundwith 4m top width and 1:1 side slopes. Rock bund willstart by filling of boulders from the one end ofdiaphragm wall.

3 Temporary earth fill : Filling of temporary earth fillforcofferdam and entrance gate will start parallel to therock bund.

.4 Interlocking sheet piles : Driving of interlocking sheetpiles will start from the east side the south dock with thehelp of crane with vibro hammer on completed portionof temporary bund.

5 Capping beam : On completion of top pluggingexcavation along the interlocking piles will be carriedout for construction of capping beam.

6 Anchoring works : The main application ofgeotechnical ground anchors is to prevent horizontalmovement and ensure stability of retaining structuresincluding sheet pile, bored concrete pile and steeltubular pile walls.

Working inside 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.

Poor environment.

Safe environment.

Design responsibility

Easy work.

Re-usability of materials.

Cofferdams are temporary structures and used in cases where the plan area of foundation is very large, depth of water is less and for the soft soils, where soils allow easy driving of sheet piles.

While significant progress and achievements have been made in the field of geotechnical finite element mechanics, further advancements are necessary. On the practical side, as computational power increases it is expected that three dimensional software programs will be come increasingly popular and more affordable. Hence, human judgment is by far the most important aspect of finite element analyses of cofferdam excavations.