Differences 5.8 -> 6.0

Why are my non-restrained embed depths less in 6.0 than in 5.8 ?

You might notice that for embedment depths greater than 12' you will get shallower calculated depths in Version 6.0.

The difference is due to a change in the way the program calculates the allowable lateral pressure when checking for a 12' limit.

Please see code sections 2006 IBC 1805.7.2.1 and 2007 CBC 1806A.8.

The item to look at is the definition of "d":

"Depth of embedment in earth in feet (m) but not over 12' for the purpose of computing lateral pressure."

Also note the definition of "S1" :

Allowable lateral soil-bearing pressure......based on a depth of 1/3 embedment....:

In Version 5.8 of the SEL this was interpreted as meaning that the allowable lateral soil pressure was limited to that of a 12' deep embedment, which resulted in a maximum allowable lateral pressure of  12 ft / 3 = 4 ft * allowable lateral pressure per foot of depth. By a strict read of these definitions it appears this is the meaning, however reasonable engineering judgment of this unclear definition raises doubts that it is not correct because of it's over-conservative results

After much discussion and review of other & older versions of this calculation it was determined that the proper usage was to limit the maximum allowable lateral earth pressure to that at 12' of embedment. So in Version 6.0 this equals 12 ft * allowable lateral pressure per foot of depth.

In general, to limit allowable lateral earth pressure to that at four feet below the earth surface just seems far too conservative.