Hello, I have been going crazy trying to figure this one out. Hopefully someone can help.

I am solving a soil mechanics question using a method called Simplified Bishops Method:

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Please note in the formula for Ψ that F = F.S.

The two equations are dependent on each other. I have tried using goal seek and Data Solver but can't seem to get it to work.

Please see excel sheet attached. Thanks in advance!

Bishops.xlsx