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CD vs CU(bar) Triaxial Testing

CD vs CU(bar) Triaxial Testing

(OP)
A soils testing firm is suggesting that CD testing is not required for a stability analysis of a silty clay compacted embankment soil; rather just CU(bar). Indicating that CD testing is rarely performed. Is there a justification for not performing CD testing for drained conditions on compacted clayey soils (i.e. can CUbar testing be performed instead and would the results be similar)?

My experience says not, but I'm curious how others are addressing)

RE: CD vs CU(bar) Triaxial Testing

Ran properly the consolidated undrained test with pore pressure messurements, CU bar, will give you the same results as a consolidated drained test, CD. The lab needs to be experienced running these tests since they can be tricky.

The advantage to you and the lab is that a CUbar test can be ran in a couple of week or less whereas a CD test on clay could take months to run. This equates to quicker test results at a much lower cost.

It has been years since I've seen a CD test performed.

Mike Lambert

RE: CD vs CU(bar) Triaxial Testing

Consolidated Undrained (CU) and consolidated drained (CD) tests only refer to the fashion in which the testing is conducted. The two will both provide you with effective strength parameters. As GeoPaveTraffic mentions, the CU is quicker to perform. The CU test also has the advantage that it provides you with a useful stress path.
I only recommend CD testing to clients when they request triaxial testing on a dense sand (to exactly establish where failure occurred) or in special circumstances where the Poissons ratio of the soil is specifically sought after.
Approximately 95% of all triaxial testing we conduct is CU testing.

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