Coffer Dams
A cofferdam is a type of
watertight construction designed to facilitate construction projects in areas
that are normally submerged, such as bridges and piers. One is installed in the
work area and water is pumped out to expose the bed of the body of water so
that workers can construct structural supports, enact repairs, or perform other
types of work in a dry environment.
In some regions of the world, this
construction is better known as a caisson. Working inside a cofferdam can be
hazardous if it is installed improperly or not safely pressurized, but advances
in engineering have led to increased safety for workers using this unique work
environment.
A variety of materials can be used to construct a
cofferdam, which is truly a feat of engineering. Although it is a temporary
structure, it must reliably hold water back from the work area and also
withstand very high pressures in order to be safe, and the construction is
often used as a project for engineers learning their craft. The most basic type
uses sheet metal, which is pounded into the bed of the body of water to create
a watertight wall. Next, pumps are used to pull water out of the enclosure so
that it will be dry. Some are built from wood or concrete, while others use a
double walled mechanism, with filler made from aggregate materials in between the
two walls.
The walls of a cofferdam can extend all the way to the
surface of the water, leaving it open at the top, or it can be built as an
enclosed structure. In very deep water, enclosed and pressurized ones are used
for worker safety, while in shallower bodies of water, an open structure can be
used. Workers access a closed cofferdam through hatches and tubes, and care is
taken to make sure that the air supply is consistent and the pressure is kept
at a normal level.
Shipwrights and repair yards also use a portable
version, which can be attached to the side of a ship to enact repairs below the
waterline. At sea, this can be a useful way to quickly address potential
problems until the ship is taken into dry dock for more long-term repair. Minor
repairs can also be undertaken with a portable one in a shipyard to avoid the
expense of hauling the ship into dry dock for the work to be completed.
