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RE: Drilled Pier Minimum Diameter

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What about small diameter foundations for small
construction projects?  I often design small footings
for decks for townhouses,etc.  These usually end up at
approx 10 to 12" diameter with 1 to 4 10M bars(#3).
Gary



On 15 Oct 2004 at 10:55, Sherman, William wrote:

> ACI 336.1-01 states that it applies to drilled piers of 30-inch
> diameter and larger. This was based on potential physical entry into
> the shaft for inspection. Smaller diameter piers are not specifically
> "disallowed", but the document does not provide requirements for
> smaller piers. I questioned this limitation of the document during the
> public review period and the committee said that they would consider
> this as new business for future revisions. I noted that "18-in and
> 24-in drilled piers are common in practice". 
> 
> Section 1808.2.1 of the 1997 UBC has a limitation on the length to
> diameter ratio but permits exceptions. I don't know of any specific
> "code" limitations for absolute minimum drilled pier diameter, but an
> article I have states "the smallest practical drilled shaft is
> 12-inches to 14-inches in diameter, with a depth no more than about 30
> feet. Typically, the ratio of the length divided by the diameter
> should not exceed approximately 30." 
> 
> My personal opinion is that the minimum diameter should be 18-inches
> for practicality in placing concrete, adequate concrete cover, and to
> minimize effects on strength if soil encroaches on the diameter. 
> 
> 
> William C. Sherman, PE 
> (Bill Sherman) 
> CDM, Denver, CO
> Phone: 303-298-1311
> Fax: 303-293-8236
> email: shermanwc(--nospam--at)cdm.com
> 
> 
> > -----Original Message-----
> > From: richard lewis [mailto:rlewistx(--nospam--at)juno.com] 
> > Sent: Friday, October 15, 2004 8:32 AM
> > To: seaint(--nospam--at)seaint.org
> > Subject: Drilled Pier Minimum Diameter
> > 
> > I am looking for minimum diameter of a drilled pier.  I was 
> > told by another engineer that is was 18" by either the ACI or 
> > the AASHTO specifications.  I looked in my copy of ACI 336 .3 
> > "Suggested Design and Construction Procedure for Pier 
> > Foundation" and didn't find any minimum diameter 
> > requirements.  My copy is outdated.  I don't have any AASHTO 
> > specifications.
> > 
> > The reason I ask is I was wondering if 12" diameter was 
> > standard practice.  I have never specified that small before. 
> >  It seems to me the rebar would be too close in a 12" diameter
> >  shaft.
> > 
> > I would appreciate any insight on this.
> > 
> > Thanks.
> > 
> > Rich
> > 
> > ________________________________________________________________
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