CU(consolidate Undrained) test on normally consolidate soil shows c=0,
can Unconfined compressive (UCC) test after consolidation be possible in the similar NC clayey soil sample?
consider dimensions of the sample are same, consolidation stresses and conditions are same.
Yes it is possible because failure mechanisms are different in those tests.
c=0 does not necessarily mean that soil does not have cohesion. only due to loading condition, the micro-mechanism responsible for cohesion is not activated.
so the answer is yes, it is possible but the bavior of soil sample would be different
Dear Respondents,
Difference in two testing
In triaxial CU the sample is under confining stress and pore water pressure develops.
In UCC, confining stress is zero and pore water pressure dissipates.
both the samples fail under compressive loading and same strain rate.
Is there any other difference? please clarify.
I think there is mistake in understanding .
In CU test the pore pressure is zero in the first part ie in the consolidation stage whereas in the second stage pore pressure develops since the drainage valve is closed.
In UCS test confining stress is zero but pore pressure does develops since the rate or strain application/loading is fast.
I am sure if UCS test is carried out after consolidation of sample it should give higher strength in comparison to a sample where it is unconsolidated.
The main difference between sandy and clayey behavior is short term-long term behavior. In short term, loads are carried by excess pore water pressure in clays. However, in long term, when excess pore water pressure dissipates there is no difference: Both NC Clays and sands use friction to carry shear.