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Re: Pole Foundation Embedment

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Some responses to your questions:

1)  S1 is a function of embedment depth and makes it an interative solution.

2)  Frost depth would not normally be deducted from the effective embedment
depth.  The design should be based on non-frozen soil.  Frozen ground would
normally be stiffer and not governing.   Two cautions, however:  a)  frozen soil
can cause uplift in the pile such that the embedment below the frost should
resist this and b)  it is common to ignore the top 1 ft of soil to account for a
possible loss of soil over the life of the structure.

3)   I would use the lateral bearing value at 1/3 the depth for S1 calculation,
but also check that the value of lateral bearing does not exceed the 15x value
in the table  or the 12 ft  maximum depth for lateral bearing calculation per
the definition of "d".     If this occurs, the S1 would need to be reduced to
account for the new soil pressure diagram.

And, most important, if this is a critical design or you have special
circumstances, you should consult a geotechnical engineer.

Ed Haninger, SE - but not a geotech engineer
Fluor Daniel
Aliso Viejo, CA

RajSTC(--nospam--at) on 11/09/99 11:18:24 AM

Please respond to seaint(--nospam--at)

To:   seaint(--nospam--at)
cc:    (bcc: Ed Haninger/AV/FD/FluorCorp)

Subject:  Pole Foundation Embedment

I have difficulty in interpreting pole foundation embedment formula given in

Required depth, d, of embedment is a function of S1, which is defined as
"Allowable lateral soil bearing pressure as set forth in Table 29-B, based on
a depth of one-third the depth of embedment."

Is it, therefore, correct to say that, S1=Allowable Lateral Bearing X (Depth
of embedment)/3?  Also, would it not be prudent to discount the frost depth
in this calculation?

One of the footnotes to table 29-B, states that the lateral bearing value
"may be increased the amount of the designated value for each additional
depth to a maximum of 15 times the designated value." So, if d=10 feet in
clayey soil, is the lateral bearing equal to 1000 psf/ft depth of embedment
or should it be an average value of (100+1000)/2 = 550 psf/ft depth of
embedment? Taking advantage of this footnote will make the solution
iterative, because while 'd' is dependent on S1, S1 itself becomes a function
of 'd'.

Any comments?  Thanks.