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re: caisson/pile

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Actually the concrete in the caisson or round pier for a short pole isn't stressed highly.   Obviously the anchor bolts are designed pretty much to the limit, but usually the size of the caisson (or pier) is determined by the soil parameters.   Sometimes the anchor rods, the template at the bottom of the anchor rod assembly and the rebar will dictate the pier diameter.   I like large diameter piers to eliminate cage and rebar conflicts and still get my clearances from the outside of the spirals to the dirt.

I never allow cold joints in my piers.  We try to excavate, inspect by the geotech, set the cage and anchor bolts, inspect by the rebar inspector and pour the concrete with the concrete inspector, all in one continuous operation.

But a number of times my geotechnical engineer will tell me he drove by one of my poles and informs me that it's been built!   That also meant that no one submitted a report to me and the building department,(required on my drawings) that the dirt was the same as in the soil report; that the passive pressure started where the geotechnical report provided: that the rebar is what I designed the project for and the concrete has the strength, type and water-cement ratio that I asked for.  (And didn't get segregated during the pour).

Of course, that contractor might have just bought the pole.


At 01:08 PM 12/8/2006, you wrote:
I agree with whoever said as long as the rebar is properly developed, the concrete pile/ shaft foundation will be OK with a cold joint. The concrete is not doing much structurally unless the loads are really high, which if they are 4ft in diameter I am sure they are, but normally what controls the design in sandy soils of these types of foundations is geotechnical issues. The min rebar you use is normally for temp/shrinkage and less then you need for moment.
And our mate from Down Under was correct, caissons and cofferdams should not be confused with pile foundations, but in my opinion could easily be confused with each other or in some instances are the same thing.
Caisson, hollow cylindrical or square tube used as a foundation, or to provide a working space for construction projects below ground or underwater. Caissons can be up to 10 m (up to 33 ft) in diameter and are usually made of concrete or steel. Construction workers or machines excavate soil from the inside of the caisson. As soil is removed from underneath the caisson, it sinks into the ground. The bottom edge of caissons are fitted with a cutting surface to make it easier to sink the structure.
Microsoft ® Encarta ® Encyclopedia 2005 © 1993-2004 Microsoft Corporation. All rights reserved.
Cofferdam, a walled structure used to create a dry work space in an area otherwise covered by water. Cofferdams are used in building construction and during the construction of structures such as dams, locks, and bridges. A cofferdam commonly consists of steel sheets that are driven into the ground and supported by pile-driven posts. The walled enclosure thus formed is then pumped dry so that construction work can proceed. Cofferdams must be sturdy enough to resist the pressure of the water surrounding the cofferdam. See Caisson.
Microsoft ® Encarta ® Encyclopedia 2005 © 1993-2004 Microsoft Corporation. All rights reserved.
Andrew Kester, PE
ADK Structural Engineering, PLLC
Lake Mary, FL 32746