Caisson

Details of Constructions

1. CAISSON
Fig. Views of the caisson for the New York River

2. Definition: In geotechnical engineering, a caisson is a
retaining, watertight structure used, for example, to work on the
foundations of a bridge pier, for the construction of a concrete
dam, or for the repair of ships. These are constructed such that
the water can be pumped out, keeping the working environment
dry.
Caissons may be large or small, deep or shallow. Large ones are
especially useful for heavy bridge work; small ones, for buildings
and miscellaneous structures.

Fig. cross-section of a pressurized caisson

3. Construction of caissons

4. Types of caisson:
The three main types of caisson are :-
1.Box caisson
2.Open caisson &
3.Compressed-air caisson or Pneumatic
caisson
And another special type is FLOATING
CAISSON

5. Box caisson:
Box caissons are prefabricated concrete boxes with
sides and bottom. They are set down on a prepared
base. Once in place they will be filled with concrete
to become part of the permanent works, for
example the foundation for a bridge pier.

6. Typical section of Box caisson

7. Advantages of Box caisson:
It can be used where construction of
caissons at sites is costly or not possible.
Its construction cost is low.

8. Here is an Image of Box Caisson

9. OPEN CAISSON
As its name implies, an open caisson is one that has no top or bottom
during its use as a protection for the excavation process. It is like a box with
vertical sides only, a honeycomb structure with open ends. In plan, it may
be square, rectangular, circular, or, whatever shape best suits the situation.
Open Caissons used in soft grounds or high water tables, where open
trench excavations are impractical, can also be used to install deep
manholes, stations and reception/launch pits for micro tunneling, pipe
jacking and other operations.

10. Constructional overview of Open Caisson

11. Compressed-air caissons or pneumatic caissons
A pneumatic caisson is a caisson with a
permanent or temporary roof or floor near the
bottom so arranged that men can work in the
compressed air trapped under it.
Compressed-air caissons have the advantage of
providing dry working conditions which are
better for placing concrete. They are also well
suited for foundations for which other methods
might cause settlement of adjacent structures.

12. Typical section of pneumatic caisson

13. SPECIAL CAISSON
Floating Caisson:
In certain cities and even countries the demand for land
and space is rapidly exceeding the supply. Maritime
centers do not escape from this reality, the continuous
expansion of commercial maritime traffic and activities in
seaports due to increases in international trading has
generated an increased demand for an effective use of
ports and harbors.
Port and harbor facilities from the infrastructure that makes
marine traffic possible, facilitating the construction of
vessels, its protection against wave action and, its loading
and unloading activities. In other words, they play an
important role in facilitating international commerce.

14. Some images of floating caisson

16. Special Topics:
Caisson disease: It is so named since it appeared in
construction workers when they left the compressed
atmosphere of the caisson and rapidly reentered
normal (decompressed) atmospheric conditions.
It is caused by the same processes as decompression
sickness in divers.

17. These are the following precautions should be taken to avoid
the caisson disease:
1. No person should work for more then one shift in a day and
the duration of shift should not exceed 12 hours.
2.The temperature of the working chamber should be
maintained at 25 degree Celsius.

3.The rate of compression and decomposition should be
properly controlled.
4.A medical chamber must be provided just near the side of
the work.
5.A stand by air compressing plant should be kept ready for
use in case of emergency.