Flexible Wall Permeameter
Flexible Wall Permeameter
(OP)
I'm performing a permeability test, ASTM D5084, using a 150mm dia. sample. After saturation and consolidation, the permeability test is performed using a confining stress equal to the previous consolidation. What I'm don't understand is that during the test (constant flow bottom to top), the flow is steady, the gradient is steady but the sample pressures are gradually decreasing together.
Typically, flows are 0.2 cc/sec, gradient = 2, k = 1x10^-4 cm/sec and the sample pressure is usually around 600 kpa with an effective stress of 3 kpa.
Any thoughts on why the sample top and bottom pressures would be able to maintain a constant gradient but be dropping in pressure? thanks
Typically, flows are 0.2 cc/sec, gradient = 2, k = 1x10^-4 cm/sec and the sample pressure is usually around 600 kpa with an effective stress of 3 kpa.
Any thoughts on why the sample top and bottom pressures would be able to maintain a constant gradient but be dropping in pressure? thanks





RE: Flexible Wall Permeameter
Also, 3 kPa is a VERY low effective stress. Is that the correct value?
RE: Flexible Wall Permeameter
The top and bottom pressures are being applied with flow pumps. Since the permeability test is performed at the same effective stress as the consolidation, I don't expect to see the sample still consolidating. The sample is structural backfill with roughly 6% silt. Typical consolidation runs for an hour or more until end of primary consolidation (t100). The pressure drops range between 1 - 15 psi/hr.
Assuming the sample is consolidated and there are no leaks, what other causes could exist?
Thanks
RE: Flexible Wall Permeameter
I would suggest checking the flow pumps to see that they are working properly.
RE: Flexible Wall Permeameter
I wondering if a small amount of air trapped in the flow pumps could be responsible for this...?
Thanks
RE: Flexible Wall Permeameter
RE: Flexible Wall Permeameter
You do not need to worry about consolidation you keep the difference of confining pressure to back pressure less than the effective overburden pressure. Bring up the confining pressure to about 80 psi and saturate the specimen. You can run the test at lower pressure. This may explain the unusual readings since there is air in the sample.
RE: Flexible Wall Permeameter
RE: Flexible Wall Permeameter
You are right. No problem. 3 psi effective stress sounds Ok, I guess if there is concern about consoliding the sample.