auger-cast pile

[v2]

what is the best approximation in determining the ultimate moment for the vertical reinforcing design in auger-cast piles when the geotechnical engineer has reported to you the allowable compression, tension and latteral capacities only?

 

[ishvaaag]

For ordinary buildings here a practical approach was taken using common recommendations in a "Technological Norm" NTE. No calculation is made respect the reinforcement, it extends I think to remember 6 m down, the reinforcement being standard for the size. It is being used successfully that I know, but of course is NO calculation.

From your data you may for lateral loads bracket through assumed lateral moduluses of subgrade reaction consistent with the allowables capacities of the soil in the layers, that I would be taking between 1/4 to 1/2 of the vertical ones or so.

 

[dlew]

v2,

The location and magnitude of the maximum moment in piles subject to lateral loads depend on the type of soil (cohesive or cohesionless) and on the type of restrain at the top of the pile (free or fixed against rotation). There is a wide variation between these cases.

The book "Drilled Pier Foundations" by Woodward,Gardner and Greer has a clear (and lengthly) explanation of all these cases and the corresponding formulas.

AEF

 

[dlew]

v2,

You can also get info. on piles subject to lateral loads on the Federal Highway Administration site:

http://www.fhwa.dot.gov/bridge/geopub.htm#drilledshafts

Look under drilled shafts and pile foundations. Some publications can be downloaded. Check the download time, some of the downloading may take hours.

AEF

 

[Ron]

Have your geotechnical engineer give you the point of lateral fixity for the pile. From there you can compute the moment and the reinforcement required. The reference dlew gave will show you a method for determining.

If the geotechnical engineer has the capability to run "L-pile", this software can conveniently give you the maximum expected loads and moments, as well as the point of fixity. From there, it becomes a "cantilevered column" design.

 

[JAE]

Lpile per Ron is good.

Also - we typically do not design for lateral forces in auger-cast piling as they typically are quite small in diameter (14" to 16&quot as compared to drilled piers (18" dia to 96" plus dia.). Lateral forces in structures with auger-cast piles are usually taken out by other means than using the piling.

 

[dougantholz]

JAE, I have to respectfully disagree with you. Lateral loads are often taken out of the building via the ACP's. They are small in diameter, but usually require pile groups of 4-5 for moderately sized buildings. If not, plenty of tie beams will be necessary. With a center bar reinforcing you should be able to get the bending moment out of the pile.
Here is a tip to watch out for. On ACP's they usually say you can put a center bar down 20' after the pile has been poured. Check your moment at the end of that bar (minus development length of course) and make sure that you don't have a problem. In the Missouri River Valley we often have 50-60' long piles with significant moment in the top 30'.
HTH
Doug

 

[JAE]

Doug,
Perhaps you're right, but the small diameter doesn't get you much soil resistance capacity. Almost like a knife through butter if you're dealing with poor soil.

Do you treat the groups of piling as a whole or calculate individual lateral capacities for each?

 

[dougantholz]

If it is a two or three pile group, we treat them individually. If it is 4-6 then we treat them as a group. They don't have much capacity, but then again the Cs values we have in Missouri are usually around .06-0.1.