to the cofferdam wall. It also provides watertightnesswhen filled with earth and rock.Movable cofferdams of timber, steel, or concretehave been built, but their uses and designs are verysimilar to those discussed under boxes and opencaissons, below.CaissonsCaissons are boxes or chambers used forconstruction work underwater. There are three formsof caissons used in constructing foundationsunderwater: box, open, and pneumatic caisson. If thestructure is open at the top and closed at the bottom,it is called a box caisson. If it is open both at the topand the bottom, it is an open caisson. If it is open atthe bottom and closed at the top, and compressed airis used, it is a pneumatic caisson.It is sometimes difficult to distinguish between acofferdam and caisson. In general, if the structure isself-contained and does not depend upon thesurrounding material for support, it is a caisson.However, if the structure requires such support assheathing or sheet piling, it is a cofferdam. Retainingwalls and piers may be built of boxes of wood, steel,or reinforced concrete, floated into place and thenfilled with various materials. These are known asfloating caissons. Open caissons may be constructedof wood or steel sheet piling.The preceding information provides only a basicunderstanding of heavy construction. As with otherphases of construction, specialized tools andequipment will be required. The Table of Allowance(TOA) at your command will have these items. Followall safety rules and manufacturers’ recommendationsfor operations and maintenance.RECOMMENDED READING LISTNOTEAlthough the following referencewas current when this TRAMAN waspublished, its continued currencycannot be assured. You therefore needto ensure that you are studying thelatest revision.Pile Construction, Field Manual 5-134, Headquarters,Department of the Army, Washington, D.C., 1985.10-17
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