Coffer dams are temporary structures built to retain water and soil in order to create a dry work area for construction projects. There are several types of coffer dams suited to different conditions, including earth-filled, sheet pile, and cellular designs. Key considerations in selecting a coffer dam include water depth, area size, soil/river bed conditions, and potential for erosion or flooding. Proper design is needed to withstand hydrostatic pressures and ensure structural integrity until the permanent structure is complete.

1. COFFER DAM

2. Contents
 Definition
 Uses
 Selection of Coffer Dams
 Types of Coffer Dams
 Design features of coffer dams
 Leakage Prevention
 Economic Height

3. Definition
 Cofferdams are temporary enclosures to keep out water
and soil so as to permit dewatering and construction of
the permanent facility (structure) in the dry.
 A Coffer Dam 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.
 Meaning of Coffer Dam : Coffer = Box
 To take up the Foundation works in the Marine Region,
it is necessary to obstruct the water flow by means of
Coffer Dam.

4. PURPOSE TO USE COFFER DAM
STRUCTURE
 To retain Soil & Water
 Can be used as either Temporary or Permanent
 Main purpose is to provide dry working area for workers
 It is constructed to facilitate pile driving operations.
 It is used to place grillage as well as the raft foundations
 It is used ,when the foundations for piers and abutments of a bridge,
dams, locks, etc. are to be constructed.
 Some times it is also provided to store water temporarily.

5.  Cofferdams can be used in all the sectors as explained below.
 Civil Engineering: Underground Car Parking, Foundation,
Basement Construction
 Transport Engineering: Bridge Pier, Support Walls, Ramps,
Ground Water Retention, Tunnel Work etc.
 Water Engineering: Weirs, Culverts, Flood Protection
Walls, Scour Protection Walls, Securing Embankment etc.
 Port Construction: Dock Works, Jetty Works etc.

6. SELECTION OF TYPES OF COFFERDAMS
1. Low heads of water – earth fill cofferdams
2. Narrow Excavations – single wall sheet
pile cofferdams otherwise double wall
cofferdams or cellular sheet piling are
suitable for wide excavations
3. The materials available at site of work for
construction
4. The possibility of overtopping by floods,
tides, etc. and sliding – rock filled crib
cofferdams

7. 5. The nature of bed on which the cofferdam is to rest –
deep deposits of soft clay, A heavy earth filled crib
or cellular cofferdam could not be suitable but
single wall sheet pile would be required in these
conditions.
6. The nature of velocity of flow,i.e. water flowing with
slow current or with swift current
7. The chances of bed erosion due to reduction of water
way caused by the construction of a cofferdam.
8. The facilities available for the transport of equipment
and material required for the construction of a
cofferdam.

8. Types of Coffer Dam
1.Earth fill cofferdams - mainly for low level water
2. Sand Bag Coffer Dam – to divert coarse of water
3.Rock fill cofferdams
4.Timber Crib or rock filled crib cofferdams -
Construction on land and than floated into place,
which is also known as Gravity Dam
5.Braced / Sheet Pile Coffer Dam- Consisting of Sheet
Piles, mainly used in shallow water depth
(i). Single wall coffer dams
(ii). Double wall coffer dams
(iii). Cellular cofferdams
6. Movable or suspended cofferdams

9. EARTH FILL COFFERDAMS

10.  Suitable for rivers or streams having shallow depth of
water, about 120 to 150 cm, with low velocity of flow
 It is the simplest type of cofferdam.
 Free board – 60 to 90 cm
 Top width of earth dyke – one meter
 Suitable side slope should be provided
 Provided suitable drain
 Its depends on soil availability and site conditions.
 Dry conditions – clay embankment provided
 Wet condition – sand materials suitable

11. ROCK FILL COFFERDAMS

12.  The construction of rock fill cofferdams is similar to
earth fill dams
 It can be constructed with steeper slopes
 Water depths – 3 m.
 In case of high heads of water , this can be achieved
by a clay or concrete care wall
 Impervious layer provided(concrete or caly corewall
or sheet pile ) for reducing entry of seepage

13. TIMBER CRIB OR ROCK FILLED CRIB
COFFERDAMS

14.  It consists of timber cribs made from logs of wood
 Constructed on land and floated into place
 It consists of a unit or a cell open at the bottom and
having the framework of horizontal timber members.
 Hollow space thus formed are then filled with rock or
gravel
 Depth of water – 10 to 20 m
 Used for wide excavation and rocky river bottoms

15. SHEET PILE COFFER DAM
1. Single wall cofferdams
-it used in places, where the area to be enclosed is very
small
-depth of water is more = 4.5 to 6 m
- A single row of sheet piles is provided on the whole length
of the cofferdam
- Guide piles, Wales and struts (wood)
- guide piles are first driven deep in the river bed and
spacing between them 1.8 to 3.0 m
- The sand bags are stacked on the inside and outside faces
of the sheet to increase the stability of cofferdam

17. Use of Guide Block to prevent
twisting of Sheet Piles

19. 2. Double wall cofferdams
- when the area to be enclosed is large it is
necessary to provide double wall cofferdam
- The double wall cofferdams are of two types:
(i) Ohio – river type cofferdams
(ii) timber or steel sheeting cofferdams

23. 3. Cellular Cofferdams
- The cellular cofferdams are mostly used for
dewatering large areas , where the depth of water may
be 19 to 21 m.
-Mostly used the constuction of marine structures like
Dams ,Locks etc.
- The two common shapes of the cellular cofferdam
are:
(i) Circular type
(ii) Diaphragm type

29. MOVABLE OR SUSPENDED
COFFERDAMS
 Where there are numbers of repetition
work in under water foundations ,such
as in the piers of multi span river bridges
, it is economical to design the
cofferdams to be moved as a single unit
from one foundation to another.

30. DESIGN FEATURES OF COFFERDAMS
 The design of a cofferdam depends on various factors such as.
(i).Hydrostatic head of Water
(ii).Dimensions of the area to be covered by the cofferdams
(iii).Subsoil conditions
(iv).Fluctuations or of outside water level
(v).Possibility of erosion
(vi).Presence of ice
(vii).Floating logs(the stem of a cut-down tree, etc.

31.  A purely theoretically designed cofferdam may fail
for factors unaccounted in its design.
 Therefore ,become necessary to combine practical
knowledge or experience with the theoretical aspects
in the design of a cofferdam.
 For width and Depth of cofferdam :
for H < 3 m, W = W
H > 3, W = 3 + ½*(H-3)
Where, W = Width of cofferdam in
metres
H = Height of water above river bed
in metres

32. Construction Sequence of
Coffer Dam :
1.Driving of Guide Frame
2.Lowering of Sheet Pile
3.Driving of Sheet Pile
4.Horizontal Bracing (Waller & Strut arrangement) to
withstand the load coming on sheet piles from outside.
5.Excavation and Plug in Concrete to resist uplift pressure
6.Reinforcement and Concrete work of the Permanent
Structure

33. COFFER DAM
• Factors governing the Economic Height of Coffer Dam
• 1.Depth of Water
- Low depth => Earthen Dam
- High Depth => Sheet Pile Coffer Dam
• 2.Current and nature of flowering of Sheet Pile
- High Current => Sheet Pile Coffer Dam
(Higher Seepage Control Capacity)
- Low Current => Earthen or any other Dam
(Less Seepage Control Capacity)

34. • 3.Type and Period of Work
- Short Duration Work => Timber Dam
- Long Duration work => Sheet Pile Coffer
Dam
• 4.High and Low Tide Level of Reservoir
- Sheet Pile must have top level slightly higher
than that of the HTL. So that even in
extreme case water can not over top the
coffer dam, to achieve the dry working
through out the season.

35. • 5.Scour Level of Reservoir
- Scour level can be considered as the bottom
most layer of the loose soil of river Bed Level.
- Up to Scour level there are chances of erosion
due to the current of water. In any Pile or Well
foundation, the care to be taken that the
founding level must be below the scour water
level
• 6.Type of Material to be used
- Structural Sheet pile is costly but can be reused
at different projects.

37. SHEET PILE COFFER DAM
• Some Photographs

46. GAMMON INDIA LIMITED
CABLE STAY BRIDGESURAT
AP-02 (EXCAVATION WORK)

47. Bracing welding work in
progress

51. SHEET PILE COFFER DAM
• Some Photographs