useful for students about dams

1. TYPES
OF
COFFERDAMS

2. COFFERDAM
Cofferdam is defined as a
temporary structure which is
constructed to remove water
and/or soil from an area and
allow it for further work.

3. TYPES
Single wall
cofferdam
Double wall
cofferdam

4. SINGLE WALL COFFERDAM
This type of cofferdam is used
in a place where the area to be
enclosed is very small and it is
suitable up to a maximum
depth of water of 25m

5. COMPONENTS
Guide piles
Longitudinal runners
Bracing frames
Steel or wooden sheet piles.

6. CONSTRUCTION
The soft material lying over the
river bed is removed.
Timber piles known as guide
piles are first driven deep into the
firm ground below the river bed
Longitudinal runners called Wales
are then bolted to the guide piles
at suitable distance apart

7. Then steel or wooden sheet piles
are driven into the riverbed along
the Wales and are secured to
Wales by bolts.
The sheets on the two faces are
braced by the trussed arrangement
of struts.
The cc spacing of piles may vary
between 1.8 to 4m

8. Half – filled sand bags are
stacked on both the faces of the
sheets
After the construction, the water
in enclosed area is pumped out
and further work is taken up.

11. A cofferdam consisting of two
lines of sheet piles are tied to
each other, and having the space
between is filled with sand.
This type of cofferdam is used in a
place where the area to be enclosed is
very large and depth of water is high.
DOUBLE WALL
COFFERDAM

12. COMPONENTS
Vertical guide piles
Horizontal Wales
Sheet piles
Tie rods
struts

13. CONSTRUCTION
The guide piles are first driven
deeper in the river bed.
The Wales running horizontally
are fixed between the guide piles.
Then sheet piles are driven along
the inside edge of Wales to a
fairly impervious strata.

14. The soft material from the bottom
of the cofferdam is dredged out.
The space between the sheet piles
are filled with puddle which may
consist of an intimate mixture of
sand or clay and gravel
A berm of clay may be provided
on the outside of the cofferdam to
avoid leakage.

15. The width of cofferdam should be
decided by considering structural
stability, degree of water
tightness, space required for
placing machinery etc..
 For H < 3m , W=H
 For H > 3m , W=3+ 1/3 (H – 3)
W= width
H= height of water above the
river bed.