Pore pressure measurements during an Unconsolidated Undrained Triaxial Test

[Thilanki]

Hello,
Is it possible to measure pore pressure during an Unconsolidated Undrained Triaxial Test?

 

[LRJ]

The UU test is a total stress test in which you're (usually) only interested in the deviatoric stress versus axial strain response. As such, measuring the PWP response is unnecessary; this is why UU testing equipment doesn't generally come with the ability to add PWP transducers.

You could do a UU test in some stress path equipment (i.e. the equipment in which you'd do consolidated undrained triaxial testing) and be able to measure the PWP response as standard, though I'm not sure why you'd want to do that: if you're going to the effort to measure PWP then you ought to do a consolidated test and get a representative response; the UU test will likely not give you a representative PWP response.

Why do you require the PWP response from a UU?

 

[fattdad]

yes.

f-d

ípapß gordo ainÆt no madre flaca!

 

[EireChch]

I have little experience with triaxial testing. However, I had a discussion during a job interview recently and the topic of triaxial test came up. I stated that a CU test is generally most common as it provides total and effect stress parameters. He said thay they typically run UU test and measure PWP. He called it the "poor mans CU" as it gives effective stress paramters and said that some people argue that its not as accurate as a CU but he was happy enough with it.

I thought to ask that if youre going to measure PWP why dont you just to a CU test? for the sake of the extra day?

Interested to hear opinions, do other people adopt/agree with the above?

 

[Okiryu]

Thilanki, are you doing this for sand soils? Perhaps you are trying to evaluate PWP generation due to rapid loading (i.e. earthquake loading)?

Anyways, I also have little lab experience with TX tests but I tend to agree with EireChch - if you want to measure PWP, I would go for CU tests.

 

[fattdad]

Yeah, I don't agree at all, but it is possible. Shearing rates for UU testing are not suited for PWP measurements.

f-d

ípapß gordo ainÆt no madre flaca!