Overconsoildation pressure /negative skin friction

[dccd]

I was told that negative skin friction of the clay can be ignored if the overconsolidation ratio = preconsoildation pressure / overburden pressure now > 1.4



However, I cant find any proof on this ? Can someone help to explain this ?

 

[EireChch]

I have never heard of such a rule.

Negative skin friction occurs when the soil around the pile settles more than the pile its self.

I can see the logic in that an OC CLAY should have minimal settlement (compared to NC CLAY) so the potential for negative skin friction is reduced. However, an OCR of 1.4 is a normally to lightly over consolidated CLAY.

 

[geotechguy1]

I guess if the OCR is high you'd expect the clay to be very stiff and thus not settle much, but then, 1.4 isn't a very high OCR and I doubt more than 5mm of movement is required to generate some negative skin friction