Triaxial test - sample saturation
Triaxial test - sample saturation
(OP)
I'm running a CU test and I'm not sure I fully understand the process of driving the air into solution.
The way I understood it is: same pressure is applied at the top and bottom of the sample and the air driven in the solution is not drained out of the sample. A colleague is telling me that we should create a circuit where water flows from top to the bottom of the sample and carry air dissolved into solution out of the sample.
Thank you
Dan
The way I understood it is: same pressure is applied at the top and bottom of the sample and the air driven in the solution is not drained out of the sample. A colleague is telling me that we should create a circuit where water flows from top to the bottom of the sample and carry air dissolved into solution out of the sample.
Thank you
Dan





RE: Triaxial test - sample saturation
Flowing water won't do it and it'll take you a long time to realize you failure (i.e., you'll get bad pore pressure measurements during the shearing of the sample.
In summary: You are correct and your colleague is not quite right.
f-d
¡papá gordo ain't no madre flaca!
RE: Triaxial test - sample saturation
Upon setup of the triaxial cell and sample mounting, some air inevitably is trapped within the lines and possibly in the porous stones. A very small gradient along with a very small effective confining pressure and leaving one side (usually top) of the sample open to draining can flush out some amounts of air, alleviating the need for large amounts of back pressure to drive the air into solution during the sample saturation phase. I usually apply 2 or 3 psi cell pressure (depending on OCR), 1 psi back pressure to the bottom and drain the air out of the cell/sample from the top at atmosphere. One burrette of water is sufficient normally.
Partially agree with fattdad: colleague definitely not quite right, but if you have flow during the shearing you are probably not running an undrained test. "Flow" should cease after consoldiation phase is deemed complete.