Caisson Construction
Webster’s dictionary defines
a “caisson” as ”…a watertight box for underwater construction work.”
Municipal Builders utilizes this type of construction to
construct a deep structure in an area with either tight site
constraints or poor soil conditions.
This method of construction is usually used as a cost
effective alternate to the need for “sheeting” as a soil retention
system. This method is
only cost effective if an open hole is not a viable option for the
construction of the structure.
In general structures utilizing this method are 25 to 70 feet
deep or deeper. Sewage
lift stations are the most common structure of this type.
Drawing off John’s experience with Barbarossa and Sons, a
pioneer in this type of construction, Municipal Builders started
pursuing caisson work early in its history.
Here is how this method works:
1)
A structure is designed with the inside dimensions
desired by the design team.
The structure is designed with an open bottom and “cutting
shoe” which forces all of the earth below the structure to the
inside as it “sinks” to its desired elevation.
The structure is poured in manageable vertical lifts and the
structure is excavated from the inside utilizing a clam bucket on a
crane.
2)
As the structure sinks more vertical lifts are added and the sinking
operation continues. The
ground water is allowed to seek its own level within the structure
and the vertical excavation continues thru the groundwater within
the structure. No
dewatering is necessary.
3)
Once the structure is sunk to the proper elevation a concrete
plug or “trieme” is poured in the bottom of the structure below the
water which is left in the structure at its static level.
4)
Once the “trieme” or concrete plug has cured the water is
pumped out of the structure and a finished bottom is poured on top
of the trieme plug. From
this point on conventional construction practices are used.
As stated above this method of construction
becomes cost effective only when conventional “open cut” methods of
construction is not possible due to site constraints or poor soil
conditions.
Municipal Builders has extensive experience in
this type of construction.
We possess the experience required to be responsible for the
design and implementation of the processes used to correctly
construct a structure in this manner.
Potential difficulties include:
-
Keeping the structure straight as it sinks into place.
-
The ability to advance the structure to its desired elevation and stop it once you achieve the correct elevation.
-
The ability to provide a watertight structure upon completion.