I've never seen a "good" answer to this problem, even though I've designed several over the years.

I just looked at the load from the back wall being transmitted to the side walls in shear. Then you have to make a judgement to whether you can take that shear into the soil.

There may be other ways of looking at this problem, but this is what i've done in the past.

Mike Lambert

Thanks. Its the judgement part that I am most concerned about. I guess if the sheet pile wall was ridgid then the soil shear capacity calculated as a failure plane on the back side of the piles would give me an indication of its suitablility or not.

Frictional resistance I think would be the only other way I can to resolve the issue.

Hmmm

When we did cofferdam work on interstate highway contract along CT. shoreline we had four sided cofferdams with inside wales; at their intersections, we had welded additional diagonal bracing members and essentially acted as stiffening rings. The load on the sheet piles was strictly shore line water. In your case, with three walls, that system will not work well unless the load is not significant, so you'll need to anchor the walers, perhaps only on the two outside walls.

"...and essentially acted as stiffening rings..." should have been "...and the whole system essentially acted as stiffening rings..."

thanks chicopee. The system is essentially your highway cofferdam halved, three sided, all framed with diagonal struts. the load transfer to the side walls is not a problem as shear cleats carry the transverse waling load into the side walls. Its the further transfer of that load into the soil that I am strugling to find a design model for.
I have, since my first post carried out some calculations based on shear strength of soil x active area and the theory is the same as my designers approach so I am going with that.
Surprising that I cant find any other examples of this method on the Web!!

A lot of these calculations are done by the contractors' engineering staffs. While these in-house calculations are job specific, these calculations would normally be submitted to the State (who would be the client) for review if the jobs are state funded. If you were to review customers' literature provided by sheet pile anchor manufactuters, you should be able to find typical calculations. Do a web search of geotechnical designs and you should get a lots of hits.

No one has mentiomned the most important consideration. What is on the 4th side of the cofferdam? Where is the lateraL load from the long side going? The wales for the two short sides also act as bracing for the long wall. The loads in the corner braces or from the long wale need to go into the short side wales. The axial forces in the two short side wales need to be resisted. Sometimes, these axial loads are taken out along the side walls, if they are long enough. If the side walls are too short, this disipation may not occur. Usually, the axial loads in the two short side wales need to be supported by a 4th sheeting wall or by an existing structure on the 4th side, opposite the long wall.

www.PeirceEngineering.com

The basis of the problem is the fact that the system is 3 sided. The short side wales will be welded to the side walls and I am relying on soil shear strength * contact area of sheet pile to resist them.

Once calculated my resistance is close to 6 times the transmitted load so I am relatively satisfied that the scheme is safe. Just havent been able to find any text or previous examples to confirm the theory.

I thought this thread was closed and opened up the discussion again here:
http://www.eng-tips.com/viewthread.cfm?qid=370587

Seeing as how this is still open:

When you say "soil shear strength" what do you mean by this?
Are you using cohesion or are you using a friction angle with some sort of normal force?
Thanks!

EIT
www.HowToEngineer.com