Define the term "caisson" and discuss about types of caissons.
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What is Caissons?
The term caisson is derived from Latin, which means box or case. Caissons are hollow inside and usually constructed at site and sunk in place into a hard bearing stratum. Often the caissons have high construction cost and their construction is restricted to major foundation works.
Caissons are used for bridge piers, abutments in rivers and lakes, docks and wharves, break water and other shore protections works, and large water front structures such as pump houses subjected to very heavy vertical and horizontal loads.
a) Open Caissons (Well foundation)
In open caissons or well foundations the top and bottom are kept open during construction. The caisson is sunk in place as grab buckets through water remove soil. Upon reaching its final position a concrete seal, usually 1.5 m to more than 4.5 m thick, is deposited through watera) Open Caissons (Well foundation)
In open caissons or well foundations the top and bottom are kept open during construction. The caisson is sunk in place as grab buckets through water remove soil. Upon reaching its final position a concrete seal, usually 1.5 m to more than 4.5 m thick, is deposited through water.
b) Pneumatic Caissons
The top of pneumatic caisson is closed and contains a working chamber as shown in Fig.2 at which pressure greater than atmosphere is maintained. The compressed air used to exclude water from entering the working chamber enables the excavation. Concreting is to be done in the dry condition.
Box Caissons
The box caissons are closed at the bottom and open at the top as shown in Fig.3. They are usually fabricated on land, floated to site and sunk in position. While sinking sand, gravel, concrete or water are filled inside the caisson. This type of caisson is suitable when hard strata are available at shallow depth. Sometimes false bottom made out of wooden planks are also used for floating.
The term caisson is derived from Latin, which means box or case. Caissons are hollow inside and usually constructed at site and sunk in place into a hard bearing stratum. Often the caissons have high construction cost and their construction is restricted to major foundation works.
Caissons are used for bridge piers, abutments in rivers and lakes, docks and wharves, break water and other shore protections works, and large water front structures such as pump houses subjected to very heavy vertical and horizontal loads.
a) Open Caissons (Well foundation)
In open caissons or well foundations the top and bottom are kept open during construction. The caisson is sunk in place as grab buckets through water remove soil. Upon reaching its final position a concrete seal, usually 1.5 m to more than 4.5 m thick, is deposited through watera) Open Caissons (Well foundation)
In open caissons or well foundations the top and bottom are kept open during construction. The caisson is sunk in place as grab buckets through water remove soil. Upon reaching its final position a concrete seal, usually 1.5 m to more than 4.5 m thick, is deposited through water.
b) Pneumatic Caissons
The top of pneumatic caisson is closed and contains a working chamber as shown in Fig.2 at which pressure greater than atmosphere is maintained. The compressed air used to exclude water from entering the working chamber enables the excavation. Concreting is to be done in the dry condition.
Box Caissons
The box caissons are closed at the bottom and open at the top as shown in Fig.3. They are usually fabricated on land, floated to site and sunk in position. While sinking sand, gravel, concrete or water are filled inside the caisson. This type of caisson is suitable when hard strata are available at shallow depth. Sometimes false bottom made out of wooden planks are also used for floating.
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