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RE: Uplift on Belled Drilled Pier

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Within Bowles' Foundation Analysis and Design this subject is discussed
in sections 16-13 and 4-11.

>From Section 16-13:  "The pullout resistance can be estimated using the
shaft skin resistance + the pile weight and the method of Sec 4-11. If
the soil is reasonably competent and the base enlargement is on the
order of 2D, the pullout capacity of the pile should be about 2x the
shaft skin resistance plus pile weight."

Equations are presented in section 4-11 which are NOT based the
truncated quasi-conical soil pull out zone observed in model and full
scale testing. The equations do include the effects of the footing and
soil weight as well as passive pressure friction resistance on a
cylindrical surface defined by the diameter of the footing (or bell
diameter in your case) with additional factoring based on shape and
internal friction. The equations estimate an ultimate capacity and
should be reduced by an appropriate factor of safety.

If you would like more info, please contact me privately. Thanks.


Brent R. Koch, P.E.
Koch Engineering, Inc.
Livermore, CA

-----Original Message-----
From: richard lewis [mailto:rlewistx(--nospam--at)] 
Sent: Thursday, November 13, 2003 08:18 AM
To: seaint(--nospam--at)
Subject: Uplift on Belled Drilled Pier

I am working on a drilled pier foundation for a pre-engineered metal
building.  There are significant uplift loads on the frames.  I will be 
belling the bearing ends of the piers.  For uplift resistance I know I
can use skin friction.  But for the bell contribution, how is uplift
resistance calculated?  Is it the weight of a soil wedge based on the
angle of friction?



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