what's the maximum height above grade for cast in place drilled pier?

[delagina]

i usually use about 1' above grade but if my equipment skid is 4' above grade and say drilled pier is 7' below grade.
i'm curious how they pour this in construction.

 

[jayrod12]

A sonotube. One the hole is drilled the shove the sonotube into the hole and then pour it full. Some bracing to keep it plumb but otherwise that's all you need

 

[delagina]

My question is should I put a steel column instead of projecting the drilled pier 4' above ground.

 

[theonlynamenottaken]

I'd avoid unnecessary connections if possible, but a pier embedmentrojection ratio of less than 2 is definitely pushing it depending on the soil, the magnitude of lateral loads, and the pier diameter. A connection of some type to the skid is unavoidable but you'll need an additional bracing connection or a moment connection if you switch from concrete pier to steel column above grade.

If the soil can take it and the anticipated lateral deflection is acceptable then resisting lateral loads wholly through pier flexure and shear (no steel column) is easy to design and detail.
Do you have p-y curves from a geotech to do pier design?
Is an integral slab at grade or grade beams between piers possible? Either of those would help avoid having a braced or steel moment frame between grade and skid.

 

[delagina]

I'm interested in construction if it's easier to have steel column or drilled pier 4 or more feet above grade. Is there a maximum height for sonotube above grade that it's better to use steel column for simple skid equipment foundation?

Of course on structural design I can design that either of these situations will work.

 

[MotorCity]

A drilled pier with a projection of 4' above grade is a rather small projection, just make sure your formwork or sonotube can withstand the lateral pressure of wet concrete.

How many drilled piers do you have, 4? 400? If you only have a few, I doubt that you would see any significant difference in cost regardless of which method you choose.

Also, if you extended the drilled pier up 4' above grade, does that eliminate a trade (i.e. steel fabricator and erector)? If not, and you will be erecting steel anyway, again I say the difference in cost is negligible.

 

[Retrograde]

I would stop the pile at ground level, construct a pile cap and then build a column (steel or concrete) off that. Depending on the relative dimensions of the column and the pile you could possibly omit the pile cap.