Thanks for the info!
However...
My question regarding Hansen's method arose because I'm using the USACE Cofferdam manual and going through all the examples. I found a lot of numerical errors, all typos, though... The Pile Buck manual, from their literature on the web looked liked it reprinted material from the Corps and NAVFAC and other sources, but I may end up getting it anyway (I have two Pile Buck books and they're very good). Anyway, Hansen's method is graphical and since I'm not of a steady hand, I have to cheat. I also have questions about just how to start drawing the logarithmic spiral's axis vs. the centroid of the failure surface - which I approximated by drawing an oblique parabaloid tangent to the centroid of the sum of the cofferdam's fill. I got close to the manual's answer, but that wasn't good enough for me...
What I really would like is a photo essay of an engineer completing the solution so I could watch a "pro"...
I put together a spreadsheet mimicing the graphical results and it's a bit closer, but there are a lot of unanswered questions that a computer program might give me more insight on. For example, the Corps' manual's example for a cofferdam on rock has answers I get pretty close to and since it's my scaling vs. the book's maybe I'm off, but the prescence of typos (incl. transposed numbers) leads me to believe that there's something missing. The manual doesn't state the scale of the drawings, but it sure looks like 1:20 - though I'm 1.5 ft off on one of the answers.