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Boussinesq analysis

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Mike,

Peck, Hansen & Thornburn, 2nd edition, has charts relating values of n (depth
below crest of wall) to H*rho/q', where H is height of wall, rho is the
pressure at depth n that a line load exerts on the wall, and q' is the line
load set back from the back of the wall a distance, m*H.  Reference is given
to tests by Gerber (1929) and Spangler (1938).

Spangler's "Soils Engineering," gives the formula for pressure due to a line
(strip) load as:

   hsubl = 1.27*p*(x^2)*z/Rsub1^4

where,

   hsubl = horizontal unit pressure at any point on wall, in pounds per
         square foot

   p = applied strip load, in pounds per linear foot

   x = horizontal distance line load is from back of wall

   z = vertical distance from top of wall to point where horizontal pressure
      is to be calculated

   (Rsub1)^2 = x^2 + z^2

HTH

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Michael Hemstad wrote:

. > We are analyzing an existing foundation wall for
. > lateral load based on a changed vertical load adjacent
. > to it (we built up a pedestrian plaza with increased
. > dead load and pedestrian live load where the street
. > used to be).  We used equations from the textbook by
. > Das (Principles of Geotechnical Engineering) for strip
. > load surcharge.  They are the same in the 2nd Edition
. > (eq 5.38) and 3rd Edition (eq. 10.81) and include a
. > term involving q/H, where H is the wall height.

. > We gave it to an EIT to check.  When he pulled out his
. > textbook (Das, 4th Ed.) the term in the equation
. > (6.40) was q/pi.  I tend to believe this one, because
. > the units work out correctly.  Since our wall is 26
. > feet tall, our original analysis was off by a factor
. > of about 8.

. > The only other textbook we have available (we're stuck
. > in a satellite office), Bowles, does not deal with
. > this topic.  Can anyone confirm one or the other of
. > these equations for us?

. > Thanks.

. > Mike Hemstad

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