For Normally consolidated clays, what is the virgine curve? 1

[ZooKaa]

Hi,
I had a hard time trying to understand the meaning of the virgin consolidation curve for NC clays. I understand that Virgin means that all the present effective stresses acting on the soil are larger than the preconsolidation pressure of the soil, therefore the e-log(P) curve will be linear with no curvature at all, but its slope is not the same slope of the linear part of the e-log(p) curve resulted form 1D consolidation test on the same clay. WHY IS THAT??????

 

[jdonville]

ZooKaa,

All clays tested in the lab are overconsolidated to one degree or another. This is because the act of removing the sample from the ground alters the state of stress and the sample will rebound somewhat from the in-situ state, depending also on the degree to which moisture is permitted to enter/exit the pore spaces of the material.

This behavior permits estimation of the preconsolidation pressure from the e-logp curve. If the preconsolidation pressure is close to the effective overburden pressure at the depth of the sample, it is called NC.

However, obtaining a sample without disturbing it is extremely difficult and relatively expensive. Additionally the sample preservation and preparation can influence the shape of the resultant e-logp curve significantly. Thus, the shape of the curve, even in the "virgin" range can be quite a bit flatter than the true (or theoretical) in-situ e-logp relationship.

Therefore, it pays in critical situations to exercise great care in obtaining, preserving and preparing the sample for testing.

Hope this helps.

Jeff

 

[ZooKaa]

Thanks jdonville