Cellular Cofferdams/Hansen's Method 1

[DaveVikingPE]

I'm new to cellular cofferdam design/analysis. I'm studying the graphical method to determine a factor of safety against rotation using Hansen's method. Is there a mathematical method? Are there computer program(s) that may aid in this area? I'm more interested, at the moment, in learning/studying Hansen's method as opposed to having a need for design assistance, so I'm interested in anyone's comments. Thank you.

 

[derubertis]

You might refer to "Theoretical Manual for Design of Cellular Sheet Pile Structures (Cofferdams and Retaining Structures)." The manual was produced by the Waterways Experiment Station of the Corps of Engineers in 1987. I don't know if it has been updated or if it is available online from the Corps of Engineers. I contains a good discussion of Hansen's method for slip on a circular failure surface. If you're new to cellular cofferdam design and analysis, you might be interested in securing a copy of "Cellular Cofferdams" published by Pile Buck, Inc., PO Box 1056, Jupiter, FL 33468-1056, 407-744-8780. It contains the Corps manual in its entirety.

 

[DaveVikingPE]

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.

 

[ishvaaag]

Respect to mimicking graphical methos for geotech, logarithmic spiral inlcuded as surface of failure, I have implemented and posted such thing in Mathcad for slope stability. The sheet by itself defines iteratively through parameter trial surfaces till find the sought one.

So maybe you want try Mathcad as programming environment, is quite friendly.

 

[DaveVikingPE]

Argh! I have MathCAD version 6... Oh well.

I'm stuck going through the example of a cofferdam on rock in the USACE manual. Because of the numerous math errors and scaling inconsistencies contained in the example, I'm just not able to satisfy myself that I have, in fact, reached the right answer. The example of a cofferdam on sand doesn't appear to have the errors this one does, though it would be nice to achieve closure before I move on.

 

[DaveVikingPE]

Update...

I bought myself a nice little W-5 C-Thru rular/protractor that's got nice, long lines defining angles (cost was $0.89 US - Pearl Paint, NYC). And I, through determination and right of force (i.e., hitting myself in the head and kicking my butt), have mastered the method. I also picked up the crucial (to me) paper by Lacroix, et al. on cofferdam design, aiding me in my quest.