agressive ground

[Karlos80]

Hi,

I have a project where the Site Investigation indicated extremely acidic ground conditions with PH = 2. In the BRE special digest they say that anything below 2.5 is a problem. A contractor also highlighted that these conditions are very difficult for construction ??

Cheers

 

[manstrom]

That is extremely acidic. I would bet that this would increase corrosion of steel amongst other things.

When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller

 

[PEinc]

So, do you have a question?

http://www.PeirceEngineering.com

 

[IRstuff]

pH = 2 is around the pH of stomach acid, so I would think that in addition to any problems with construction materials, personnel would need to wear PPE, especially feet and hands.

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[cvg]

yes, it will make construction difficult. primarily from safety concern but also corrosion of steel. for instance the equipment will be damaged by the corrosion unless it is cleaned off frequently. steel pipe and structural steel will corrode. the workers will be affected - eyes, throat, lungs etc cannot tolerate exposure to acid. try squirting lemon juice in your eye, that would be the same ph.

 

[Karlos80]

PEinc,

My question is how to design and construct a building in a such acidic environment? Any guidlines or codes you guys are aware of to apply here or maybe some advises based on your previous projects?

thx

 

[ACtrafficengr]

Is that the natural pH, or is it contaminated? Is neutralizing the acid an option?

 

[EngineeringEric]

Wow. I'd hate to be civil contractor for this one. I would think this is something that cannot be just-provided information out of the blue. This should require major input from the Geo and Architect and Owner and is going to be an additional change order for all. As it not something that a special kind of concrete can fix 100%.

 

[Karlos80]

We suspect that the acid is humic, coming from the peat which is present in the gravel directly below the peat, probably from oxygen getting below the peat when the groundwater level falls. Sulphate levels are low. However, based on the BRE document the humic acids are generally not below 3.5!

It seems unlikely that the acid is from man made contamination, as the soil strata are all natural (peat and gravel) sulphate values are low…

Also not all the boreholes show ph 2, there are some which indicate ph 8 so huge range here.

 

[dhengr]

Karlos80:
Could you dig the whole site out to a few feet below the bottom of footing elev. and line it with a heavy rubber/plastic membrane? Then fill and compact back up to the footings, slabs, etc. Essentially the same as they line a solid waste dump site, but for the opposite results, to keep the bad stuff out.

 

[oldestguy]

I'd involve an agronomist or soil scientist, since there may be a practical solution, such as incorporating basic materials naturally. They do these balancing acts all the time for crop growing.

 

[Ron]

This will severely attack any concrete, steel or combination thereof used in construction. Not a good site.

 

[racookpe1978]

So: Lots of problem statements, but no solutions yet. Criticize the following please.

Plumbing: Use poly pipes for sewage away from the building; will a septic system even work in peat/swampy areas?

Water supply? Plastic pipes as well? Above ground water pipes?

Power: Telephone poles are going to fail? Going to last? Need 12 to 6" of concrete (no rebar!) around them to get to the house?

Pilings up to a suspended "above water" type wood-only structure, with a house on top of the platform?
Big thick concrete slab, and everything in the slab? Or will rebar corrode inside the slab over time?

 

[BigH]

Notwithstanding racookpr1978's fist line - are there other buildings in the area? Then someone else had this problem before and local knowledge is best. Has the acidity been double checked? Is it based on one or two samples? Could the test results actually be outliers? We get them all the time in other testing . . .

 

[Karlos80]

Lads,
In relation to the building it is a large structure (Court House). The structure needs to be piled due to bad ground conditions.

Almost each borehole indicates a low ph =2 , 5 meters below ground.

There are existing buildings in this area and we have never heard any issues but we were not the designers of those projects so it is difficult to say what approach they undertook.

 

[Guest262653]

Since this is a real issue, which may induce large additional costs, wouldn't it be wise to run some more soil tests in a different lab?

 

[darthsoilsguy2]

i don't have any advice on structure... apart from thinking a non-reactive all-purpose membrane and good detailing could work. but i will say that pH is just one of the tests done on soils that we consider part of the "corrosion series" when we're are testing samples. our typical data output is:

Sample Location
Depth
Visual Classification (or you can full USCS it)
Natural Moisture Content
Resistivity AASHTO T-288
pH AASHTO T-289
Chlorides EPA Method 9056A*
Sulfates EPA Method 9056A*
*I usually would not have the EPA methods run if the resistivity was above 3,000 ohm-cms and the rest of the info seemed good

i haven't come across soils that acidic so i haven't had to deal with it professionally, but my first comment would be to make those other tests.

 

[darthsoilsguy2]

there are probably better references out there, but this is one that i've downloaded and skimmed through before.... If it doesn't help you, it might help the person whose search on aggressive soils ends up here

http://www.nature.nps.gov/geology/soils/Understanding Soil Risks and Hazards.pdf