Limits for Retaining Wall Analysis

[EngWade]

When designing/analyzing retaining walls, at what distance(both uphill and downhill) of the wall does the analysis need to extend? I had a professor once tell me that when designing a retaining wall, anything (and everything) on the upside and downside of the wall has an effect. However, while this may be true in the classroom when theory rules, I believe there has got to be a limit where practicality sets in, and you no longer need to consider loadings at a "sufficient distance" from the wall.

I've attached a sketch illustrating my question. In my sketch I've labeled the two distances I'm curious about (x1 and x2). A "rule of thumb" I've developed based on my own reasoning is to extend a distance equal to the stem (height of the wall) behind the heel of the wall, and then extend at a 45-degree angle upwards. The area this would encompass I would consider to be my "area of influence" on my wall. This coupled with the Factor of Safety has been enough for me in the past (as I've worked on relatively short walls to date). Similarly, at what distance downhill (x1) would the analysis be sufficient?

Any guidance or things I'm missing on this would be greatly appreciated.

Thanks so much for your time.

 

[fattdad]

Geology has too much of a factor to simply address your question. If there is a stiff fissured clay below the wall, you'd need to consider wedge type failures as well as the more conventional circular failure. I don't like the downhill slope at the toe either. I'd think you sketch doesn't go far enough in either direction. It's pretty easy to add more to either side, however.

f-d

¡papá gordo ain’t no madre flaca!

 

[EngWade]

This is strictly a hypothetical situation. But I think I might be following, that you agree with my professor, in that everything is dependent upon everything else, and there is no real way to determine the "area of influence" as I had sketched out.

 

[concretemasonry]

Walls/footing size analysis and a global soil situation are different worlds. They both have to be looked at.

I have seen curved 40' high segmental retaining walls (SRWs) built where the critical item was the global situation that affects the geogrid design and placement. Obviously, no concrete footings were used. Since the length of the varying height walls (4' to 40') was about 10 km, the engineering was critical and quite sophisticated.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.