Drained conditions on slope stability

[Gimbli]

Do you know if there is any empirical correlation, paper or research on obtaing c' from SPT data. If you can give some light about; i'm trying to do a slope stability analysis. I know how to estimate peak phi, but, how can I estimate c'. I don't think it should be equal to zero when working with cohesive soils, Medium to stiff cohesive soils (MH as per USCS), when drained condition should govern. Am i right?

 

[BigH]

Remember that c' - phi' is a mathematical model. In almost all cases, c' really does equal zero at the appropriate normal stress levels - but at normal working stress levels, in forming your failure envelope, you do have, what I generally call, an apparent cohesion. (in residual and critical states, it is zero). There is, to my knowledge, no relationship that has ever been established between c' and SPT. Sorry.

 

[Gimbli]

Thanks for your opinion. Thought the relationship did not exist because I have never found it. IS apparent cohesion a standard value range?, say 50 to 200 psf? This is the range I usually select. Is there any maximum apparent cohesion? I found once two publications that recommended c' for compacted soils. Right now I may tell one of them was a NAVFAC but I cant tell exactly cause I'm at home. These recommended c' ranging from about 50 to 150 psf for compacted clays.

 

[geoatl]

you may need to look into undrained condition for cohesive soil.