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More on retaining walls

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In response to Stan Caldwell's comments on retaining wall design, the reason 
Retain Pro has 12 yes/no options for alternate design procedures (Stan 
Caldwell pointed out two) is that there are differences of opinion on many 
design assumptions, in addition to toe and heel design. For example, 
application of the vertical component of active pressure for a sloped 
backfill could be used to reduce sliding, reduce soil pressure, and/or reduce 
overturning (I prefer only the latter), but since various texts offer 
differing positions, Retain Pro must give the designer a choice so he/she can 
exercise judgement. In a telephone conversation with Prof. Bowles a year or 
so ago, regarding his changed position on these issues between the 4th and 
5th editions, he stated (and I'm paraphrasing) that after spending a lifetime 
studying soil behavior, he still could not definitively predict its behavior. 
Retaining wall design is easy, once you make procedural assumptions. Like the 
recipe for tiger soup--first catch the tiger. 
Regarding designing heels for bending, remember that no matter how wide the 
heel or depth of soil overburden, or counteracting upward soil pressure, its 
moment cannot exceed the imposed stem moment. This axiom is often overlooked 
when designing the heel.
We too are advocates of the Meyerhof "rectangular pressure block", which Mr. 
Caldwell mentioned (see Bowles' 5th edition page 236. It is also mentioned in 
Peck, Hanson, Thornburn's Foundation Engineering, 2nd Edition, page 314) and 
we will be including it as an option in the next Retain Pro release -- and 
hope building departments will permit it. It results, generally, in somewhat 
less toe bending moments.
And BTW, Retain Pro, while sold separately in both a Basic and Professional 
version, is also included (Basic version) in Enercalc's Structural 
Engineering Library, Version 5.1.

Hugh Brooks, SE
Retain Pro Software 

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