Non-expansive clays?

[joenorm]

There is a lot of talk about expansive clay and the havoc it can cause on structures.

But what about the rest of the clays? Do they not expand and contract at all? I imagine there is a spectrum.

 

[EireChch]

I think all clays will expand due to the introduction of moisture, but as you said the spectrum is levels that do not really affect foundations to levels that can cause hundreds of millimiters of expansion which can crack slabs, deflect retaining walls etc..

it depends on their mineralogy. For example clays made up of large amounts of Montmorillonite (think bentonite) are generally the wort offenders. Bentonite pellets can swell to 10 times (or something) their size

 

[pelelo]

There is an expansion potential criteria summarize by Robert Day in his foundation engineering book. See attached.

Expansion Potential (EP) depends on plasticity, water content, and other lab tests.

The most common criteria to confirm if clay is expansive is by doing Atterberg limits. In my opinion if clay is expansive based on Atterberg I would run additional lab tests just to double confirm.

 

[Bobby46]

My area doesn't really have an issue of expansive clays. We have soft, sensitive clays. When disturbed they lose all the shear strength and turn into soup.

Clay in this area is generally saturated at all times, so it does not see the swelling that a dry clay experiences.

 

[joenorm]

Bobby46-

How do you address this type of clay when building on top of it? Can you place a foundation without “disturbing it” and generally not have problems?

 

[MTNClimber]

Sounds similar to Presumpscot clay in Maine. Card house style structuring that's very sensitive. I've only seen deep foundations used.

 

[Bobby46]

Presumpscot and Boston Blue are the two big clay formations we see. They are essentially the same thing.

Deep foundations, ground improvement, and preloading/wick drains are the common ways around it. Deep foundations and ground improvement send the building weight to rock so the clay doesn't "feel" anything. Preloading takes all the settlement out of the clay before you build the building.

 

[fattdad]

it has to do with the diffuse double layer of phyllosilicates. Anybody recall, T-O-T?

How the topic of swelling morphed into sensitivity is confusing to me!

f-d

ípapß gordo ainÆt no madre flaca!

 

[Bobby46]

"But what about the rest of the clays? Do they not expand and contract at all? I imagine there is a spectrum."

 

[Okiryu]

Not all clays are expansive. It will depend on their mineralogy. I would check with the local geotechs to see if expansive clays are an issue in the area where you are working...

 

[joenorm]

Thanks.

I have heard of no reports of expansive clays in my area, people build on them with traditional foundations (not piers) all the time.

However, as an owner/builder being on clay still has made me nervous, probably unwarranted and just worrying as usual.

It's funny how people talk about clay, saying how dangerous of a material it is to build on, but I imagine it gets its bad rep from the "bad" clays like ones that are expansive or as mentioned about, highly sensitive. It must be one of the most built-on substrate in the world, correct?

So it would lead me to believe there are a lot of types of very "stable" clays as well as the reactive type.

 

[fattdad]

In Richmond, Virginia, we have a sensitive marine clay that supports multi-story buildings in the heart of the city. Leo Cassagrande published geotechnical foundation studies in the '50s (took the train down from Boston) related to drilled shafts on the Calvert formation. In more recent years, we now install belled (double belled) caissons in this same formation.

Not all clays are bad.

We just have to understand soil behavior, but that's supposed to be our job anyhow!

f-d

ípapß gordo ainÆt no madre flaca!

 

[csigeo]

Expansive clays in arid environments typically cause the most problems as it is the change in moisture content of the soil that causes it to expand and contract. For example the southwest states of the US (Texas, Arizona, Nevada, Colorado & California) all suffer the effects of expansive soils. These areas are dry for most of the year with rainy seasons. So you build lightweight structures on top of expansive clays, introduce landscaping and irrigation and the rainy season and all of sudden the clays expand causing damage to the structures. Then the soil dries out and contracts as the season changes. The problem is once water starts moving underneath slabs, it can't really escape and so as the years go on the soil beneath slabs/foundations absorbs more and more water causing more heave and associated damage.

 

[Lomarandil]

My question is, as someone with no geological knowledge and little access to it in my region (Southeast Asia), is there a better indicator of the swelling potential of clays than asking around about historical performance?

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just call me Lo.