Effect of Acid on Soil
Effect of Acid on Soil
(OP)
I am working on a project where a structure has settled, likely as a result of concentrated sulfuric acid in the soil. pH values are as low as 1.6. Some of the bedrock in the area is limestone and has likely been affected by the acid. Does anyone know of any publications that discuss the effect of acid on soil?
Thank you!
Thank you!





RE: Effect of Acid on Soil
I'd think that a strong acid would certainly be neutralized by the limestone and that in turn could result in loss of volume or settlement. That said, if you have a pH of 1.6 there is obviously nothing at that location that's acting as a buffer so that would not foretell of loss of volume.
Consider a layer of soil that is nothing but quartz sand. If you were to leak concentrated sulfuric acid, you'd not expect any chemical reaction or loss of volume. So, in that environment, you'd not expect a problem (and you'd have high pH values in the quartz sand layer). At this point (i.e., by your original post), it's not clear how the limestone is playing into this concern, other than by implication.
You got my interest. . .
f-d
¡papá gordo ain't no madre flaca!
RE: Effect of Acid on Soil
Thanks for the response. It is a unique project.
The subsurface conditions consist of about 10 feet of fill overlying clay and gravel layers. We may have encountered bedrock at 80 feet. Some of the bedrock in the area is mapped as limstone and would definitely react with the acid. I'm trying to find out whether the acid would affect other types of soil. I haven't been able to do any lab testing to determine mineral content of the soil.
Some of the upper (2 to 3 feet) of soil appears to have been affected by the acid, however much of the lower soil still has very high SPT values and does not appear to have been affected. The pH of 1.6 is at a depth of about 25 feet.
RE: Effect of Acid on Soil
Secondly, do you have any idea of the pH at or near the bedrock?
You might want to look at concrete deterioration in the footings and foundations before you worry about the bedrock.
RE: Effect of Acid on Soil
I'm more worried about the surficial soil and its support capability than the bedrock.
We performed more than 30 pH tests in the field during drilling and found the shallow soil had pH values in the 1.6 range. The pH values at depth were in the range of 7 to 9.
Deterioration of the existing concrete and whatever will be used to fix this is definitely a concern.
RE: Effect of Acid on Soil
What method did you use to measure pH? Did you do any other chemical characterization?
Any further insight on the source of the sulfuric acid?
Any data on the strength/compressibility of the fill? Any soil classification data?
f-d
¡papá gordo ain't no madre flaca!
RE: Effect of Acid on Soil
The gravel layers are very dense. The clay is medium stiff to stiff. The fill is predominantly gravel which is loose to medium dense.
The source of the acid is the facility. The acid has seeped into the ground over time from spills.
RE: Effect of Acid on Soil
You may want to look at the composition of the clay layer to determine the expected long term reaction with the acid from the fill material in the upper layers. - Don't poke any more holes in the clay than necessary.
If this is the case, the limestone is effectively protected by the clay layer.
RE: Effect of Acid on Soil
RE: Effect of Acid on Soil
Acids can cause deflocculation in clays, but at the level of pH you noted (7 to 9) I would not expect any effect on the clays.
You will likely need to treat the soil in the area of the foundations (lime treatment to raise the pH) so that concrete deterioration is reduced. Make sure you specify extra cover on the rebar and specify and obnoxiously require high density in the concrete.
RE: Effect of Acid on Soil
Regarding settlement if the facility has been there for some measure of time, the fill's not likely a bad actor. If this is a newish facility that sprung a leak, I'd consider poorly-compacted fill leading to settlement and see if that could result in a leak.
I like guess work from the comfort of cyberland!
Good luck.
f-d
¡papá gordo ain't no madre flaca!
RE: Effect of Acid on Soil