Bentonite

[MEM1]

Can someone tell me how to calculate the amount of bentonite required to be mixed with different soils to reduce permeability to a given level? Any help is greatly appreciated.

Scott

 

[Focht3]

It's a trial and error thing. No cookbook available.

Why do you ask?



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[iandig]

I was involved in a project where bentonite was added to a sand to produce an impermeable (<1x10-9 m/s) liner for a landfill. An 'average' amount of bentonite was addedd and samples taken for testing, the result was that a fixed amount is NOT the way to go. Even a soil which appears very uniform, can and will vary to the point that some will have too little and not function.
One of the tests that was used as a quick indicator, was the plastic limit, if the plastic limit could be reached, i.e. sufficient fines within the blended soil to allow a thread to be rolled, on a glass plate etc..., then it was deemed that sufficient bentonite had been added. The problem was the Contractor had allowed a max amount in his estimate, and he was VERY reluctant to add more than this. In the end the project was put on hold, but I do know at least one University in the UK is undertaking research into bentonite addition to sand and the resultant permeability

 

[MEM1]

Here is Kansas, we are required to meet certain seepage rates for lagoons at animal feeding operations, anywhere from 0.10 to 0.25 inches/day. With some soils, bentonite or fly ash or someother additive must be added to reduce the seepage rate to or below the specified limit. NRCS will run soil samples and then let us know how much bentonite is required in lbs/sqft/4 in thick lift. I was just curious as to how this is calculated. As Focht3 indicated, it is trial and error. This is what I was expecting. The problem I am running into, is NRCS is quite busy and it could take up to a month to get these results. Other labs I've used are faster, but they don't give us the required bentonite application rate.

Thanks again
Scott