Hey, but what about those Incan stacked walls?

posted Dec 22, 2015, 1:01 PM by Amy Stone
When discussing stacked limestone retaining walls, I frequently get reminded about the Incan walls in South America.  Those have stood for thousands of years, right?  
And, always willing to do research to provide a better product to a client, I looked into this topic.  Unfortunately, for hopeful owners, the short answer is no.  They haven't.  Admittedly, they have stood for several hundred years longer than anything I've designed.  However, upon further research, those lovely terraces come with some severe restrictions that differentiate them from today's typical use.
wall comparison
1- Maximum height is about 5ft.  Here is a 7 year old walking up a typical 500 year old wall.
Max surcharge load
2- nothing heavier than a llama or two.  Today's walls have to account for vehicles or houses behind them.  Those items are much heavier than a llama.  Even cows are too heavy.
incan drainage
3-Installation of a 3 layer drainage system and no clay or expansive material allowed at all.  You can see from the graphic (located here- http://www.pbs.org/wgbh/nova/ancient/wright-inca-engineering.html-thank you Nova) that they didn't use onsite fill.  They used a lot of hand labor sorting rocks to ensure that water did not build up behind the walls. 

no surcharge

4- Finally, there can't be any slope directly behind the stacked walls.  See how the ground at the top of the wall is flat?  FYI: the top one is flat for some distance.

I hope you've enjoyed a little trip down to South America to look at some historic walls.  I know this was one of the more fun postings to write.  Merry Christmas!
- Outlier Engineering