Drilled Pier Design 1

[strucguy]

I am looking for some useful references or examples on design of drilled piers. Any help in this regard would be greatly appreciated. Thanks in advance.

 

[jike]

Try ACI 336. Also, you might want to contact a local contractor who commonly installs drilled piers and ask for a sample spec.

If you have any specific questions, I will try to answer them.

 

[DaveAtkins]

In my opinion, the CRSI Manual is the best reference for this. It has tables, as well as design examples.

DaveAtkins

 

[escrowe]

Strucguy, do you mean structural design of shafts, geotechnical, or both?

 

[strucguy]

Jike and DaveAtkins -

Thank you for your response. I was able to find a copy of ACI 336 and started reading through it. I will even checkout the CRSI manual.

escrowe -
To be specific, I am looking for structural design of drilled piers. But, I am even reading though the geotechnical aspects to get a better understanding. But, I couldn't find a good example on structural design of drilled piers.

strucguy

 

[DaveAtkins]

For the most part, there IS no structural design of drilled piers. They are axially loaded, unreinforced concrete (although the top portion of a drilled pier is reinforced).

DaveAtkins

 

[escrowe]

LPILE does have a module for shear reinforcement of drilled shafts.
The usual configuration of bars is axial (vertical) about the perimeter.
It will also model cracked vs. uncracked EI.

 

[PMR06]

Check here too:

http://www.fhwa.dot.gov/engineering/geotech/library_listing.cfm

 

[jike]

As Dave says many drilled piers are designed for gravity load only (compressive). The drilled piers designed for lateral forces need to be reinforced in the upper 10 to 15 feet (until the moment dies out). Then there are the somewhat unusual drilled piers that are designed for uplift where the reinforcing runs all the way into the bell. There are also the straight shaft piers (no bells) that bear on rock.

 

[rday]

One thing to mention on reinforcing and uplift; it's not that unusual in areas with expansive soils.

We commonly reinforce piers for uplift resistance based on expansive soil action.

 

[PanamaStrEng]

I agree with Dave and jike for compression piles. No fancy design there. Only design as completely braced unreinforced section. I usually add some reinforcing steel in the upper 3 meters (about 0.5%) even if not required.
Calculated uplift and/or moment are a different ball game.

 

[frv]

I agree with the others. Piers are continually braced columns.

However, reinforcing should be taken down to the pint where the uplift forces can be transferred to the soil. Sometimes this is the entire length of the pier.

Also remember that uplift can occur at piers supporting shear walls or x-bracing.

 

[csd72]

I will typically allow for bending from the maximum tolerance allowed in the foundation code. In Australia this is 100 or 150mm (4 to 6").

Other than that is is generally designed as a short column.

 

[jike]

Although many drilled piers are designed as short columns, that is fully braced by the soil, if it goes thru soil with 3 blow counts or less, I usually design it as "unbraced" thru these softer soils. I do the same with piles.

 

[jheidt2543]

Sorry that I'm so far behind in reading this forum...

I've noted the following paper a few times before, but it is a very interesting and informative look at the problem.

You might find the paper "Analysis and Design of Laterally Loaded Piles and Caissons in a Layered Soil System", by T.R. Naik and A.H. Peyrot. It was published in the 1970's in an ASCE journal. The paper is based on a modificaiton of Broms' method and it has a very practical approach with a good example problem and a pretty extensive list of references.

Also, "Drilled Pier Foundations" by Woodward, Gardner and Greer, McGraw-Hill, 1972