Swelling Soils Due to Caustic Exposure

[patbaugh]

We have a 30+ year old caustic tank on a ringwall foundation that appeared to be sinking when compared to the containment concrete that was installed about 10 years ago. Elevation surveys over the last few years revealed that everything is actually "rising". Various points of the slab is "rising" faster than the ringwall which contributed to the illusion that the tank was sinking. Is there some type of remediation that can be done to stabilize the area to prevent further swelling?

 

[pmkPE]

First you need to determine what is causing the movement before a remedy can be prescribed. Does it make sense that the surrounding concrete is rising? Is the survey benchmark stable? And by what amount and in what time period are these changes occuring?

 

[patbaugh]

I am pretty sure that the reaction of caustic with the clay soils is the problem. We have had similar problems at another location but it was not as widespread as this one. We have been taking data since 1999 and elevation changes have been as much as +5" at various points. I haven't been able to find any recommendations on remediation options for the caustic/clay issue.

 

[pmkPE]

Isn't the caustic toxic? Would EPA approve of it entering the soil and therby be able to migrate to the water table? If so then the solution is how to stop the caustic from entering the soil (i.e. leaking from........) Stop the caustic from contacting the soil and the problem of swelling soil should disappear.

 

[patbaugh]

Chances are slim to none that we have caustic leaking into the soil now. I am wondering if this was there from a spill in the past and its just taken this long to migrate to the clay particles to react?

 

[Focht3]

Your problem has actually been studied indirectly - PhD thesis at UT Arlington in about 1995 - dealt with chemically modifying clays by an injection process. Researcher was Marshall Addison - contact Art Pengelly with Hayward Baker - he knows Marshall well, and can get you in touch with him.

I assume you are talking about NaOH and the soils are clays. If it's CaOH or KOH, then the chemical is directly interacting with the clays, and the changes will be permanent. If it's NaOH contaminated with K+ or Ca++ ions, then it's accelerating the reaction by raising the pH.

You can treat this by injecting HCl into the soil. Drastic, but it should work -



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"