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# RE: Site classification - IBC

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: Site classification - IBC
• From: "John C. Jones" <john(--nospam--at)struct-engr.com>
• Date: Fri, 30 Apr 2004 13:36:49 -0500

```By mentioning all three I did jump the gun a bit.  Thanks for the clarification.

John C. Jones, PE
Barnett Associates
Pell City, AL
205-884-5334
205-884-0099 (fax)

-----Original Message-----
From: Rick Burch [mailto:rburch(--nospam--at)conterra.com]
Sent: Friday, April 30, 2004 12:38 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Site classification - IBC

John,
Here is my understanding on how the avereraging is done:

1.  The IBC formula doesn't use blow count, shear wave velocity, AND
undrained shear strength,  you (or actually the geotechnical person) use
only one of the three.  See 1615.1.1.  It says that when shear wave
velocity data is not known, you can use N values OR undrained shear
strength values.

2. See 1615.1.5 for averaging.  The top 100 feet is divided in to n
layers, for example 20 at 5' each, and the test values at each of these
points are averaged.

3.  Section 1615.1.5 covers what to do with the rock N values.  On page
352, it says N is ... not to exceed 100, as Thomas Hunt said.  So you
might be averaging in a lot of 100s for the layers of your 100 feet that
are in solid rock.  In other words, you might have:  5 6 8 7 9 12  13
15  22  33  35 ... 100 100 100 100 100.

Rick Burch
Columbia, SC

John C. Jones wrote:

> They're involved, but are curious as well as to how the averaging is
> done.  The formula in IBC uses both blow count, shear wave velocity,
> and undrained shear strength..
>
> I did get the final results this morning and based on the above I
> wound up with C, which still makes a big difference.
>
> Thanks for everyone's help.  IBC is just getting adopted locally and
> the geotech wasn't completely sure on the averaging either.  Between
> them talking with folks and me talking with you all it wound up
> getting handled.
>
> Thanks again.
>
>
> John C. Jones, PE
> Barnett Associates
> Pell City, AL
> 205-884-5334
> 205-884-0099 (fax)
>
>
>
>

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