clay soil cohesion (c) and clay undrained shear strength (Su) 1

[PElucy]

What is the difference between clay cohesion (c) and undrained strength (Su)?
Where can I find these answers?
Thanks,
Lucy.

 

[fattdad]

Cohesion is the soil strength when the average deviator stress is zero. Undrained shear strength is the soil strength when the soil can't drain under shear stress (i.e., when there's pore pressure buildup.

f-d

¡papá gordo ain’t no madre flaca!

 

[irawanfirmansyah]

PElucy:
For clay we have undrained and drained strengths (Su and S')
Shear strength parameters for undrained strength are Cu & phi(u), whereas those for drained strength are C' & phi'. Since phi(u) is small in the range of 0 to 10 deg., it is used to be neglected, hence Cu = Su.
For geotechnical engineer, C for clay is meaningless; you have either say C' or Cu.
You can find the answer in any geotechnical book which describes about shear strength of cohesive soils, for example 'Introduction to geotechnical Engineering' by Holtz and Kovacs