PE Exam last minute Qs (NCEES geotechnical sample question need help)

[cloud69]

I posted this on a different forum, hoping to get more eyes here.

Questions regarding book "PE Civil: Geotechnical Sample Questions and Solutions" (April 2013 2nd printing)

Question 528. What is the source for the formula used in the solution, P = 2*L*sigma_v*C_i*tan(phi)?

Question 529. Where did the equation for sigma_a come from?


Please see picture URL for clarification.

http://imageupper.com/g/?S020001001F13822470112424190

Thank you very much for your help as it's driving me crazy to figure this out!

 

[FixedEarth]

528 - Check the referenced books in the back of your book. NCMA and proprietary wall manufacturer's also have their own design manuals which give the sources of the equations used. It is more important to know how to solve such a problem should it come in your exam. The effective length is the length of the geogrid beyond the failure plane. In this example, failure plane is given as 60 degrees, but in reality it is dependent on the soil's phi angle.

529- That is from Peck's earth pressure envelope for Sandy soils when you have a strutted or braced retaining wall. See "Foundation Engineering" 2bd edition, 1974, by Peck, Hanson and Thornburn.

 

[cloud69]

Thanks FixedEarth for taking your time to write.

@528: I examined the NCEES book again. No list of reference. Sometimes the solution to the problem itself list the reference. Occasionally, NCEES book throws in a problem with either obscure reference or appears like you said a manufacturer's design manual.

@529: Wow, "Foundation Engineering" is a mere $6 in paperback. First time I've come across it.