Question on Terghazi Bearing Capacity Factors

[Platypus Engineer]

I have copy of School of PE course notes that cite a book by Das (2007) for the table that shows the Terghazi bearing capacity factors. For the N gamma subscript  factor, there is a significant difference between the Das values and the ones shown in CERM. The values typically differ by about a factor of 1.5 to 2 times. The other factors have little to no difference.

The problem is that when working practice problems or exams, each factor DAS or CERM will give you one of the correct answers. So how do you know which of the factors to use ?

 

[geomane]

They will give those to you in the question 

 

[GeoDude_PE]

Welcome to Geotechnical Engineering where two people have different methods to solve a problem and end up giving two answers so far apart they couldn't possibly both be right. Then it is up to the engineer to use "engineering judgement".

As stated above those will be provided to you in the question.  Could the values being presented in the Das book be looking at Meyerhoff factors as opposed to Terzaghi factors?

 

[Will.I.Am PE]

It may be everlastingly too late for the OP, but looking at the 2017 edition of Das text, it looks like he uses N gamma values published by Kumbhojkar in 1993. If you're looking for the original Terzaghi values (which you probably would be on the PE exam), the CERM would have the "correct" values.

Bearing capacity factors come with some significant assumptions and N gamma is particularly sensitive to the assumed shape of the wedge of soil directly beneath the footing. That's why there's a noticeable difference between the two.