ASTM D5084 Test Method B - Falling Head Permeability-constant tailwater elevation 1

[Sebast_U_1973]

Is there a time constraint on the test method ? We are reviewing the results from tests performed by Others and some time periods, say less than 10 min. to complete the test once the specimen is fully saturated seems an error ? Any insight is greatly appreciated.

Thanks,

Sebast1973

 

[TigerGuy]

Much depends on the material you are testing. If you are testing a highly plastic clay, it could take a couple days after saturation period to reach a stable flow. Silts will likely progress faster.

 

[Sebast_U_1973]

Using the Unified Soil Classification System (USCS) it classifies as SM, Sandy Silt , or Silty Sand, with a portion as ML (Silt) some gravel and cobbles througout Site. Our concern is the time of actual test, another Lab performed the Falling Head Permeability with Constant Head. Said firm is reporting test which are less than 5 minutes ? Does not seem likely, Possibly soil sample was disturbed ? We are trying to come up with a range of test time to use for determining the Design K value. We are leaning towards not even considering rapid tests. The longest time is 160 minutes, with the majority of tests lasting 60 minutes. ? These times even seem too rapid. I recall performing said test and sometimes it wood take over 120 to 240 minutes to become fully saturated, then test starts and lasts the majority of the day ?

Tough call. I personally do not think the firm whom performed the testing did it under restrained lab environment following the ASTM specification? Simply because the firm who performed the tests did not report time to saturation ?

Its tough because as a ethically moral Engineer, it is hard to confront another professional firm indicating suspicion in the integrity of performing said tests. I must find the "politically correct words" as to not accuse, since I do not know all the facts.

On the other hand, being the Design firm responsible for the performance of the Onsite Wastewater Renovation System and Subsurface Wastewater Absorption System(s) [Leaching fields], This writer needs to be confident on the results of the lab performed tests.

 

[TigerGuy]

I've done old school falling head permeability tests on sands, where each set of readings took a few seconds. In the flex wall permeameter set-up on a silty sand, 5 minutes does not seem extremely fast to me. What diameter sample are they testing? What pressure head are they using? What is the gradation break-down of the material? What k value are they reporting?

Share the redacted report for better perspective of all reading this thread.

Time to saturation does not take long on a material with high permeability values. I'm used to working on clays that can take up to a week to saturate. On silty sand, I'm guessing you could run a couple of cycles through the system to achieve saturation, and then run the test with everything completed within an hour of setup.

 

[Sebast_U_1973]

Attached is the test data. We have eliminated any test over 10 ft/day and any test which ran less than 5 min. Therefore our range of values to choose from our statistical analysis yielded the following:"Thus this firm is 95% confident that the true geometric mean K lies within the interval 0.24 to 2.07."

Thank you for your insight and input.

Regards.

Sebast1973