Constant Head Permeability Test

[adidasmayo]

We are trying to conduct the constant head permeability test in the lab. However, the head is not the same when a tube is connected to the outlet drain and the tube is raised or lowered. Now I have looked everywhere and I cant find where the tube outlet should be placed with respect to the permeameter in order to get consistant results when compared to other labs. Where is the outlet tube supposed to be placed. The ASTM 2434 shows it near the top of the permeameter but I dont think it was done intentionally because there is no variable for it.

 

[fattdad]

The outfall of the permeameter represents the tailwater elevation. The constant head elevation represents the headwater elevation. The difference between these two elevations represents the deltaH (change in head), that is occuring over the length of the flow path (L).

Following Darcy's law, you have Q=kia. So, you'll measure Q, you'll calculate i (deltaH/L) and you'll measure the cross-sectional area of the sample.

Enjoy and have fun!

f-d

¡papá gordo ain’t no madre flaca!

 

[adidasmayo]

thanks a lot that makes perfect sense now.

 

[adidasmayo]

ok now that weve got the setup and everything under way I have another question. While we are taking outflow measurements the head based of the monometers increases over time. We cant figure out why this is happening. Should we wait until the head is constant and then run the test or is this supposed to happen and why?

Thanks again

 

[HSIII]

Are you using a flexible wall permeameter? Is it possible that somehow your inlet and outflow got reversed? What pressure settings are you at? Is the back pressure too high? Is it constant volume-constant head, or just constant head?

I would try referencing ASTM D5084, maybe you could get some additional information there.

Hope this helps at least a little.

 

[adidasmayo]

No it definitely is not a flexible wall permeameter. And i dont have my inlet and outflow reverese either. It is basically the set up that you can see at the Humboldt website for constant head located at

http://www.humboldtmfg.com/search.php?query=constant+head

we have the same permeameter and the same constant head tank. any other ideas?