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Bentonite as a Clay Liner Seal

Bentonite as a Clay Liner Seal

(OP)
Hello,

We are working on a project which involves installing piles inside a tank compound. The compound has a clay liner as a floor and it has a berm all the way around. Since we'll install piles we'll break the liner and so I would like to seal the area around the piles. On a previous project an engineer specified sodium bentonite. However, the sodium bentonite ended up being very slippery and a trip hazard. Can anyone please give me some help as to what kind of bentonite we should use? Is sodium bentonite too vague of a term?

Thank y ou

RE: Bentonite as a Clay Liner Seal

YOu can get bentonite as a mat with the material between an inner and outer shell You can also get it as a 'rope'. Can you use the mat to go around the piles with a couple of turns of the rope to wrap around them?

Dik

RE: Bentonite as a Clay Liner Seal

(OP)
Yeah I think they could do that as an option. I've never seen that approach. It's interesting.

RE: Bentonite as a Clay Liner Seal

Just to note, any bentonite will be very slippery once it is wet. That is just the nature of the material.

Mike Lambert

RE: Bentonite as a Clay Liner Seal

Bentonite is used as a thickener for well drilling to keep the holes from caving in. It can take on water and swell to 16 times its original volume. The particles actually are small plates many stacked together. There are electrical charges on these plates that attract water, a di-polar molecule. You are right, that by itself is a darn slippery material, certainly one you don't want to drive on as the site is prepared, or for that matter later. It has to be mixed with the local soil, even imported sand, but at a very small percentage, such as 3 to 5 percent. In order to properly mix only powdered bentonite should be used to be sure of a thorough mix. Then you run tests in the lab to see what permeability is create by different mixes. I'd stay on the very low percentage side, since too much is an unholy material. The thickness of the seal layer might be kept low by doing the mixing in place with a rotry garden cultivator. Many passes are required. Do not add water, because of possible excessive amount making mixing more difficult. You probably can perceive that bentonite attracts water and holds it even in dry climates. I have used this method to waterproof the exterior of houses where water soaks and causes wet basements, but after stripping topsoil and shaping the site. Topsoil is replaced. The way bentonite hangs onto water, that area then stays green in dry periods also, as a side benefit..

RE: Bentonite as a Clay Liner Seal

The GCL membrane sounds interesting, but would appear to be not for the problem at this site. Enclosed in geotech fabric is fine, but that fabric resistance to sunlight was not mentioned in the two references above, but they say "cover with soil". How much?

RE: Bentonite as a Clay Liner Seal

Sodium bentonite is the correct term. In the 1980's we used it, mixed similar to oldestguy's recommendations, as the liner for new bottom ash ponds at our electric generating stations. This included around driven piling. In the 90's, used the Cetco bentonite mats for the liner in additional ponds.

The key to successful, non-messy use of either the mats or the soil/bentonite mix is to contain the product between two layers of properly compacted soil. Mats or mix are placed on compacted soil. Then compacted soil, with a total thickness of at least 12", is placed on top. Without this containment, bentonite swells uncontrolled, losing the low permeability that is essential for it to be an effective liner. A side benefit... there is no slime or mess to deal with.

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RE: Bentonite as a Clay Liner Seal

gcl or bentonite mixed soil should be covered with a protective layer whether it is for a pond, landfill or tank bund, otherwise your clay liner will not last for long and it will be slippery.

RE: Bentonite as a Clay Liner Seal

My experience with a low percentage of bentonite in soil is that it acts like "soil". It will erode like any soil, but clay tends to hold things pretty well. The mix isn't real slipper at low percentages of bentonite. Mixing on this site may work with a concrete mixer, perhaps with some rocks thrown in to help. I'd do some experimenting with nearly dry soil to begin with.

RE: Bentonite as a Clay Liner Seal

(OP)
Thanks for the help and clarification everyone. We should cover the sodium bentonite with a layer of compacted soil.

RE: Bentonite as a Clay Liner Seal

OG once more.

You get the stuff at a large plumbing supply house, but using the term bentonite may confuse the clerk. A more common term is "driller's mud",vol clay, or some fancy trade name. Ypu do not want granulated type, sine it won't mix well. If considering adding a cover of "soil", why not just do the whole zone with the mix? Bentonite is cheap.

RE: Bentonite as a Clay Liner Seal

cvg:

Bentomat was the product I was thinking about... I've used it on numerous pond liners... thanks, Dik

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