Hyrdaulic Conductivity in Shelby Tube.

[rockiologist]

Has anybody tried to run Hydraulic conductivity within a 6 inch Shelby Tube granular sample? I have a client who says they cannot have a remolded sample. I told them that I am allowed to remold the sample to the same density as it was in the tube (ASTM 2434). He thinks that the granular sample will somehow be altered from an in-situ condition. I tried to explained that the particles are not being damaged just rearranged back into there original configuration.

 

[fattdad]

I would not buy your contention that you are replicating field conditions by replicating density. Too much published data shows that remolding moisture content can have order of magnitude differences on the hydraulic conductivity of a remolded sample. If you want the in-situ permeabilty take the Shelby tube, extrude it, put the membrane around it, place it into a triaxial cell and do a permeabilty test.

f-d

¡papá gordo ain’t no madre flaca!

 

[rockiologist]

The problem is that the sample is fine to coarse sand. Even when you extrude the sample directly into a membrane the sample tends to fall out and become even more disturbed. By the way the tube is extremely damaged and I only have a 6 inch section to work with.

 

[fattdad]

do a full sieve and use this correlation:

http://home.comcast.net/~fatt-dad/permeability_correlation.pdf

(please recognize that permeability is presented in 10^-4 cm/sec units and there is one axis that's D10 and another axis that's D20).

What you really need to do is a slug test. Rather than spend time and money on the Shelby tube, just do a hand auger or drill another boring and insert a PVC well screen with gravel pack and do a falling or rising head "slug" test. Here's a nice publication on how to interpret slug testing:

http://home.comcast.net/~fatt-dad/slug-test.pdf

Good luck.

f-d

¡papá gordo ain’t no madre flaca!

 

[Sudburyboy]

Google "Shelby Tube Permeameter".

There is testing equipment available to perform the test right in the Shelby tube. Never used it.

T

 

[Cansand]

If critical project why not trying to follow one of the field test :estimating the permiability on site

 

[oldestguy]

If you gotta run it in the tube, yes it can be done. I've done it many times, but fortunately used 3 inch tubes and finer grained stuff. Much easier that your tubes.

The main thing is keeping the sample intact and having proper filter on the discharge end. You may have to use a series of coarser gradations, but very likely in thin steps of larger and larger grain size. That is not likely to affect your answer. I hope the client doesn't want an answer with three or more significant figures. You'd be darn lucky to have the first one very accurate. It may be precise, but pretty wrong.

To begin with that client probably thinks getting the sample that way doesn't affect it. Right? Sounds like he needs some educating.

Send him here and let him explain it to us.

Those in-place tests are best, in my view.

 

[fattdad]

O.K. another item for discussion: How will you use the hydraulic conductivity data once you get it? If you are looking at a prominent component of laterial flow, you may really be mislead by running a test in the tube as any sublayers of finer soil will affect the vertical flow. On the other hand, if the overall mechanics of flow for the problem you are solving relates to horizontal flow, the slug test may be more relavent. As a rule of thumb, vertical permeability is typical 4 to 10 times lower than horizontal flow, owing to depositional environment.

f-d

¡papá gordo ain’t no madre flaca!

 

[rockiologist]

Thanks to everybody for all the input. This is for an environmental analysis for potential flow of contaminant. I agree with you that the infield test would be best. I have also tried to explain these points to my client and they still do not understand that to run a test from a shelby tube that you need to try and keep the shelby tube the same as when you pull it out of the box. Thanks again.

 

[fattdad]

If the contaminant is in the ground and you are looking at fate and transport, I'd ONLY consider a falling head test in a monitoring well. Please take into consideration that Darcy flow velocity is not the actual flow velocity: Darcy flow being V=ki and the actual flow velocity being V=ki/n where n= the porosity of the formation.

I love these types of problems, but they really do require wells to document the flow gradient, ground water contours and also a series of slug tests.

How deep is the water table? Is the chemical of concern heavier or lighter than water?

f-d

¡papá gordo ain’t no madre flaca!

 

[DRC1]

I agree with you. I used to do a lot of triaxle permiability testing. For sands you really almost have to repack in a membrane mold. I would feel that running the test in a shelby tube would not give you control of your lateral pressure vs vertical pressure. Also with the tube, you do not know what your B parameter is so you don't know the degree of saturatuion. If you really need to do tis, try saurating the sample and freezing it. Extrude, trim. mebrane and pop in the triaxe. Let thaw.
Good luck.