Advantages of Pneumatic Caissons- The advantages of pneumatic caissons are that all work can be done in dry and there is control over work. The foundation is prepared better and plumbness of caissons is easier to control. The concrete placed in dry condition will have good and reliable quality. The obstruction from boulders and logs can readily be removed and excavation by blasting may be done if necessary.
Disadvantages of Pneumatic Caissons- Pneumatic caissons have high cost of construction. They cannot be sunk to depths greater than 35 m because the higher pressure below this depth cannot be resisted by human body.
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.
Advantages of Box Caisson- The advantages of this caisson is its cost of construction. It is used when construction of caissons at site not feasible or costly.
Disadvantages of Box Caisson- The disadvantages of this type of caisson are that the bearing strata should be level or made level. This type is feasible only when suitable bearing stratum is available at shallow depth. Provision should be made for scour protection. The bearing stratum is often not compact.