Drilled Piers in Low PH Environment

[Ibeam]

Monday morning crisis:

A project we're doing at an industrial site utilizes 30-inch drilled pier foundations to rock. The holes have been filling up with water soon after drilling.

Environmental testing is performed for contaminents during and after drilling. The last pair of drilled holes filled with water that had a PH=2.0.

We're looking at the option of leaving the steel casing in-place to help protect the shaft. Does anyone have suggestions or know of an ACI or other reference to shed light or combat this problem? Type V Cement?

note, There has been no epoxy rebar ordered or used for this project.

 

[Ron]

This will likely cause significant deterioration to the concrete. Type V cement will not help in this case. The highly acidic environment will directly attach the cement and possibly the aggregate, particularly if the aggregate is calcareous.

I would coat the casing, and leave it in place.

 

[Ibeam]

Thanks Ron, I've been waiting for additional responses but it doesn't look like any are forthcoming. It hadn't occurred to me of coating the casing - would you recommend a bituminus, galvanized, or epoxy type coating such as an Ameron system? The layers of soil being penetrated go from fat clay to a coarse gravel/sand mix. The depth to rock is approximately 35 feet (+/- 5'). I'll probably use a hot-dip galv unless there's a reason not to.

I was really hoping that an admixture/polymer existed somewhere that took care of acid conditions. It seems like it would be more cost effective, especially if this is going to set project precident for other foundations (likely).

It's difficult to explain to the client why the added expense is necessary when they see things working without it that have been there for ages.

 

[SlideRuleEra]

Ibeam - If you know that similar installations are working, there is an explanation. If the groundwater is not moving, corrosion takes place... then stops since no "low-PH, replacement" water moves in.

Polyethylene sheeting has been used for years to control this problem with buried ductile iron pipe. Here is a better explanation than I can provide

http://www.dipra.org/pdf/polyEncasement.pdf

Adapting polyethylene encasement for drilled piers is probably not practical, but the problem may not be as bad as the PH test indicates - if there is no flow.

http://www.SlideRuleEra.net

 

[cvg]

A ph of 2 for groundwater is some serious acid. you need to investigate if:

a) your ph test was incorrectly showing such a low ph
b) you are intercepting a plume of underground battery acid...

vinegar has a ph of 2.4, lemon juice about 2.0 and water with a ph of 2 would be quite unusual. typical naturally occuring water sources are not usually below 4 - 5.

Naturally occuring acidity in groundwater comes from acidity picked up by rainfall and from the geology. You would need to have highly acidic soil / rock formations to cause this. Alternatively, somebody has been dumping haz-waste in this area.

 

[Ibeam]

Hmmmm... I pick curtain #3!

There are a number of large areas at this industrial site that are EPA designated "No Dig Zones".

There is a river that runs 100 yards from the property line, and I understand that where these particular foundations are is part of the old riverbed. They hit it at around 15 feet. Much of the site has undergone significant fill at one time or another. Soils reports show native soils starting at as much as 12-ft below grade in some of the bore holes, with loose to dense fill over the top.

Lots of History, even rumblings of an old acid pit. (Sometimes in the holes it doesn't exactly look like water)

So what is the PH of Coca-Cola?

 

[cvg]

coca cola is much higher than 2

http://www.snopes.com/cokelore/tooth.asp

 

[jgailla]

In environmental lab in college, we used a pH tester on a bottle of Coca-cola. Surprisingly, the pH was 2.5. I believe the carbonation has a buffering effect.

 

[Ron]

Ibeam...hot-dipped galvanizing and concrete are not necessarily a good combination either. If you can get a polymer or rubber-coated casing, it would be best. If not, a heavy bituminous coating will work. Don't waste money on paints...they won't work well in this case.

On the concrete side, I would specify a very dense concrete mix, with a high strength...not because of strength requirements, but for durability in such an aggressive environment. I wouldn't use calcareous aggregates...go with siliceous. Increase the rebar cover for added protection.

jgailla...call BB...he's looking for help.