Internal Failure Plane - Segmental Retaining Walls

[Brad_S]

I am currently looking to develop a spreedsheet that will help do backslope calculations for a segmented retaining wall. I am attempting to work through the Appendix B example in the back of the "Design Manual for Segmental Retaining Wall, 3rd Edition" and cannot seem to verify how they are getting a value.

The equation (NCMA EQ 7-50) from the SRW manual is the calculation for the (α[sub]i[/sub]) internal failure plane. I have ran the calculation almost 10 different times now using the numbers from their results and inputing it into the equation given and still my value is off. Does the equation 7-50 in the SRW Manual have some sort of hidden variable that is not shown? I had a fellow engineer print out a computer program output for this sort of problem and the internal failure plane that it yielded was different from the result I got from the equation as well.

I am just at a loss here because I cannot move forward until I can get a value I feel confident in and I cannot understand why this value is coming out wrong when using the given equation.

Thank you for any and all help.

 

[MTNClimber]

I'm stumped. I get 43.323 degrees by hand calcs but SRWall gets 52.311 degrees. Let me know if you figure it out.

 

[Bobby46]

Its been a while, but I remember finding a couple issues like this with examples and equations in NCMA. I think there are several spots where equations are labeled incorrectly, variables are inconsistent, and values do not make sense

 

[fattdad]

may want to check out FHWA GEC-11.

f-d

ípapß gordo ainÆt no madre flaca!

 

[MTNClimber]

I'm still having trouble with the equations provided in FHWA GEC-11 and the equation in AASHTO's Bridge Design Specification. The main reason is the wall is battered at 7.125 degrees. They only provide an equations for walls that are vertical or with face batter of 10 degrees or more from the vertical. But even plugging in 10 degrees gives me an imaginary number since the value under the square root is negative.

How are you making out with it Brad?

 

[Brad_S]

@MTNClimber
I was able to reproduce the results from the example by NCMA.

I was also able to contact someone from NCMA and they confirmed the equations and numbers so I went back and over analyzed the equation and found my problem. They pointed to a possible error or using the wrong B value and even sent back some calculations on their end, I will link that response so you can take a look for yourself as well.

I would be able to upload the quick excel calculation I made if you'd like to see that too.

 

[MTNClimber]

Ah yeah, I see my error now. No need for the excel calculation.

I've only compared my hand calcs for a wall with horizontal grades to SRWall's output. Glad to see that it appears to work for a broken back geometry too.