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RE: Standard for Number of Required Borings?

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I agree with the general ranges Jim lists: I've used one boring at the
center of small structures, and then gradually increase to borings at 2
corners, borings at 4 corners, borings at 4 corners and center, up to
regular borings at 100-ft maximum spacing. It helps if you know the
typical soil profile and bedrock strata in the area. If subgrade
conditions are too erratic, much more frequent borings would be
desirable. 

Another aspect of this is "How deep should the borings go?" With current
definitions of soil profiles for seismic design, at least one boring to
100-ft or at least 10-ft into bedrock is desirable. If deep foundations
are a likely possibility, boring depth should extend deeper than the
expected foundations. If shallow foundations are expected, I like to go
at least twice the depth of foundation with a minimum of 20-ft below
existing grade; deeper for heavily loaded structures. 

It is good to get the geotechnical engineers recommendations for
borings, but I also like to have input on the number and depth of
borings. 


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: Lutz, James [mailto:James.Lutz(--nospam--at)earthtech.com] 
> Sent: Wednesday, February 09, 2005 12:49 PM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: Standard for Number of Required Borings?
> 
> Ideally, this should be something the geotech is giving you. 
> I've seen different suggestions in textbooks for ordinary buildings. 
> 
> Maximum spacing 50 ft (Seelye)
> 
> One boring at each corner (Peck)
> 
> One boring at each corner and one in the center preferred, 
> but not less than three (Bowles)
> 
> -----Original Message-----
> From: Bill Allen [mailto:t.w.allen(--nospam--at)cox.net]
> Sent: Wednesday, February 09, 2005 10:43 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Standard for Number of Required Borings?
> 
> 
> Is there criteria in specifying/recommending the number of 
> borings required for a particular project?
> 
> The project I'm looking at is approximately 8,000 SF, one 
> story commercial building.
> 
> I *think* the architect is asking me this because he is 
> trying to get a fee from the geotechnical engineer.
> 
> TIA,
> 
> T. William (Bill) Allen, S.E. (CA 2607)

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