to the cofferdam wall. It also provides watertightness
when filled with earth and rock.
Movable cofferdams of timber, steel, or concrete
have been built, but their uses and designs are very
similar to those discussed under boxes and open
Caissons are boxes or chambers used for
construction work underwater. There are three forms
of caissons used in constructing foundations
underwater: box, open, and pneumatic caisson. If the
structure is open at the top and closed at the bottom,
it is called a box caisson. If it is open both at the top
and the bottom, it is an open caisson. If it is open at
the bottom and closed at the top, and compressed air
is used, it is a pneumatic caisson.
It is sometimes difficult to distinguish between a
cofferdam and caisson. In general, if the structure is
self-contained and does not depend upon the
surrounding material for support, it is a caisson.
However, if the structure requires such support as
sheathing or sheet piling, it is a cofferdam. Retaining
walls and piers may be built of boxes of wood, steel,
or reinforced concrete, floated into place and then
filled with various materials. These are known as
floating caissons. Open caissons may be constructed
of wood or steel sheet piling.
The preceding information provides only a basic
understanding of heavy construction. As with other
phases of construction, specialized tools and
equipment will be required. The Table of Allowance
(TOA) at your command will have these items. Follow
all safety rules and manufacturers recommendations
for operations and maintenance.
RECOMMENDED READING LIST
Although the following reference
was current when this TRAMAN was
published, its continued currency
cannot be assured. You therefore need
to ensure that you are studying the
Pile Construction, Field Manual 5-134, Headquarters,
Department of the Army, Washington, D.C., 1985.