for civil 6th sem student conatact:-8758060190

1. Subject: Advance Construction Equipment
B.E. Civil Engineering (6th sem (2016))
Topic :-TYPES OFCOFFERDAMS
Guidance by
Dr. Sandip S. Trivedi (Ph.D.- IIT Delhi)
Professor and Head,
Department of Civil Engineering,
GUJRAT POWER ENGG. AND
RESEARCH INSTITUTE

2.  Considering the material used in their construction, cofferdams may
be divided into the following categories.
› Earth-fill cofferdam
› Rock-fill cofferdam
› Single-walled cofferdam
› Double-walled cofferdam
› Crib cofferdam
› Cellular cofferdam
› Concrete cofferdam
› Suspended cofferdam or movable cofferdam
› Sandbag dike cofferdam
A cofferdam may be defined as a temporary structure that is constructed on a river or a lake
or any other water-bearing surface for excluding water from a given site to execute the
building operation to be performed on dry surface.

3.  Earthen embankment built around the area to be enclosed.
 The depth of water is very low.
 The velocity of the current is very low.
 The side slopes may vary from 1 : 1 to 1 : 2.
 A mixture of clay and sand or clay and gravel.
 Side slopes should be pitched with rubble boulders.
 Sometimes, Sheet piles are also provided for to make the cofferdam
watertight.

4. ROCK-FILL COFFERDAM
 If the depth of water to be retained by the embankment of cofferdam is of order of
3 m .
 Stone or rubble is used for the embankment.
 This construction is adopted only if the stone is easily available in the nearby areas.
 The stones are assembled in the required shape of the embankment and the voids
are partially filled with earth and stone-chips.
 On the waterside,the rockfill is to be provided with an impervious layer of earth.

5.  Area to be enclosed is small and the depth
of water is more 4.5 to 6 m.
 Timber piles known as guide piles are first
driven deep into the firm ground below the
river bed.
 Depending upon the velocity of the current
of the water in the river, the c/c spacing of
the piles may vary between 1.8 to 4.5 m.
 Longitudinal runners called wales are then
bolted to the guide.
 Steel or wooden sheet piles are then driven
into the river bed along the wales and are
secured to the wales by bolts.
 The sheets on the two faces are braced by
trussed arrangement of struts. This helps in
increasing the stability of walls against the
water pressure
 Half-filled bags of sand stacked on the
inside and the outside faces of the sheets
help in increasing the stability of
cofferdam.
 After the cofferdam is constructed, the
water in the enclosed area is pumped out
and the construction work is taken up.

6.  Double-walled cofferdam is provided in
such situations.
 Its construction is essentially the same as
that of a single-walled cofferdam except
that in place of one wall, a pair of walls
with a gap in between is used all along the
boundary of the space to be enclosed.
 This type of cofferdam can be used in depth
of water up to 12 m.
 As the depth of water increases, the wall
should be made wider in order to make it
stable against overturning and sliding.
 The distance between the two walls
depends upon the depth of water.
 At their top, the two faces of the walls are
connected by steel rods spaced at close
intervals. To prevent the leakage from the
ground below, the sheet piles are driven to a
good depth in the bed.

7. › If the stream has a hard bottom ,it is difficult to penetrate the guide piles or
sheet piles .In such cases crib cofferdam is used.
› The sheet piles are supported by a series of wooden cribs.
› A crib is a framework of horizontal timbers installed in alternate courses to
form pockets which can be filled with earth or stones.
› The length and breadth of each crib depend upon the depth of water and the
current of flow.
› The framework of the cofferdam (made from, logs of wood) is prepared on
ground and then floated to the site where the cofferdam is to be constructed.
› On the side of water ,the framework is provided with sheet pile
› Crib is then sunk to the position, the bottom of each crib is given a shape to fit
in the variation in the surface of bed rock.
› The space inside the crib is then filled with stone or any other material, so as to
make it stable against sliding and overturning.

8. › These cofferdams are suitable for enclosing large areas.
› They are used for the construction of long span bridge piers across
wide rivers or in backwater areas
› These cofferdams are quite expensive
Two types of cellular cofferdam
› Circular cellular cofferdam
› Diaphragm cellular cofferdam

9.  The circular type of cellular cofferdam has the advantage that each cell
may be filled completely to the top before starting the construction of the
next cell without causing any distortion to the shell of the cofferdam
 One cell is completely filled up it can be used for the construction of other
cells.
 Each cell acts as a self-supporting independent unit

10.  Consists of a series of diaphragm of steel sheet piles connected
 The straight diaphragm wails are connected to each other by steel piles arranged in
the form of arches on either sides.
 The radius of the connecting arcs is generally made equal to the distance between
the straight diaphragm walls. After the cells are driven to the required depth, they
are filled with earth, sand, gravel or other filling material. In this type of cofferdam,
as the diaphragm which separates the two cells is a straight wall, it is necessary to
fill adjacent cells at approximately the same rate. If this is not done, the unbalanced
pressure from the fill will distort the diaphragm (cross-walls) which may result in
the failure of the interlocks. In this respect, the circular type cofferdam has the
advantage over the diaphragm type cofferdam because in the former, it is not
necessary to fill the adjacent cells at the same time.

11.  A cofferdam is a temporary enclosure built within, or in
pairs across, a body of water and constructed to allow the
enclosed area to be pumped out, creating a dry work
environment for the major work to proceed.
 Enclosed coffers are commonly used for construction and
repair of oil platforms, bridge piers and other support
structures built within or over water.
 These cofferdams are usually welded steel structures,
with components consisting of sheet piles, wales, and
cross braces.
 Such structures are typically dismantled after the ultimate
work is completed.

12.  A portable cofferdam is any pre-fabricated water barrier
that can be transported to and installed at a project site,
oftentimes in response to an imminent or emergency flood
situation.
 barriers such as sandbags and levees do not qualify as
portable cofferdams because they must be fabricated on
site. On the other hand, cofferdams (also known as
coffer dams) DO qualify.
 Dam-It Dams, Inc. is one of just a few manufacturers in the
world that manufactures, transports and installs portable
cofferdams in a wide range of sizes to accommodate
virtually any project manager's needs.

13.  This type of cofferdam is useful if the depth of
water is small.
 Cement bags are partially filled with a mixture of
sand and clay and systematically laid around
the area in courses.