Consolidated Undrained vs Uncosoildated Undrained

[geopat69]

Hi All

Hope someone can assist with a basic query:


In the Consolidated Undrained triaxial test...Why would the Undrained shear stress value "Cu" be theorectically lower than the Cu for the same sample if tested using a Unconsolidated Undrained apparatus. Note: that the Unconsolidated Undrained test is more representative of the insitu conditions as opposed to the Consolidated undraing test.

The reason I ask is due to the following observations: In the Consolidated Undrained test, the sample is consolidated...meaning the void ratio is reduced and thus the Cu value should be higher than the insitu value. Yet in the Unconcolidated Undrained test...the Cu value is actually higher! (as shown in the attached extract from Whitlows book)

In short...I would have thought that the semi-circle would be smaller for the Unconsolidated Undrained test!!

Would like an experts opinion? Maybe the books figure is wrong??

thanks all!

 

[GeoPaveTraffic]

Sounds like a homework problem.

Think about how this figure would look at different vertical stresses.

Mike Lambert

 

[geopat69]

HI Geopave

It is actually neither homework or assignment issue at all. Rather an observation while reading up.

In any case, are you agreeing with me i.e in the way the figure is presented?

In altering the vertical stress for the Unconsolidtaed Undrained stress, I suppose you would indeed have a smaller stress circle?

But Maybe you can shed light on to why many literature text says that the consolidated undrained test gives "higher" cu values YET... the figure shows the Unconsolidated Undrained test being the higher! In this light I can only conclude an error in what the figures should be conveying.

thanks

 

[geopat69]

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