That's a RAP!

by Rob Condon, P.E., on December 09, 2022

I recently had the pleasure of spending a day in the beautiful city of Nashville shooting promotional videos for our Geopier® X1® system.  As we were wrapping up the shoot, the videographer, Paul (great guy by the way), leans over and says, “This Geopier thing is really cool looking, but how does it work?”  

What a great question Paul!  As someone that eats, sleeps, and breathes Geopier, I often forget that most folks don’t design ground improvement on a daily basis.  Heck, I bet most folks don’t even think about soil every day! Y’all don’t know what you are missing 😊.

Back to Paul’s question… how does a Geopier work?  I could jump right into soil mechanics and Mohr’s circle, but I think I would lose some of you along the way.  Maybe we start out with a simple analogy and save the technical jargon for a future blog.

At its simplest, a Geopier works by taking soft, squishy soils and transforming them into hard, stiff soils.  

As an analogy, think of the soft soils as being a cheap couch.  If you lay down on a cheap couch, the cushions distort all over the place and you wake up with a sore back or a stiff neck (getting old stinks!).  But for the most part, our bodies are flexible enough to handle the distortion.  Buildings, on the other hand, are not as flexible.  If a building were to distort like a person on a cheap couch, the structural connections could fail, and the building would have to be condemned (or worse!).

Soft, Squishy Soils

Now, what if we took those same old couch cushions and installed a bunch of very stiff springs?  We would basically be converting that soft couch into a stiff mattress!  This is pretty much what happens when we install Geopier Rammed Aggregate Pier (RAP) elements.  The Geopiers replace portions of the soft, squishy soils with dense columns of gravel while densifying the remaining soils between the piers.  The end result is a stiffened composite mass of very stiff springs (piers) surrounded by less stiff springs (soils) that work together to keep buildings from settling too much and becoming structurally unsound.  Great for buildings, but maybe not so great for sleeping…

Pier Reinforced Soils 

To take this analogy one step further, you can think of Geopier reinforced soils as being more akin to one of those fancy Sleep Number mattresses.  By adjusting the length and spacing of the piers, we are able to vary the stiffness of the pier-reinforced soils under the building so that the soils are stiffest in the areas with the heaviest loads.  That way we can create a customized engineer solution that meets the needs of the structural engineer while delivering a cost-effective solution to the owner.

Engineered Solution

Hopefully, this simplified explanation has given you a better understanding of how Geopier solutions work. Obviously, the actual installation and mechanics are much more complex, but I think the analogy outlined herein gets the big picture across.  

Key takeaways:
•    Geopier takes soft, squishy soils and transforms them into stiffer, harder soils.
•    Geopier elements act like stiff springs and work with the surrounding soils to support buildings.
•    Geopier creates custom engineering solutions to reinforce areas that need it most and provide a cost-effective solution that meets project team’s needs.

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