young's modulus of soft clays

[lvkb]

Can anyone give me a typical value of the undrained young's modulus (Eu) for very soft alluvial clays with an undrained shear strength of about 10kPa?

I'm trying to calculate the immediate settlement of a rock embankment on such a material.

Thanks!

 

[fattdad]

maybe 50 to 75 tsf?

¡papá gordo ain’t no madre flaca!

 

[SmokeyBear]

For normally consolidated or slightly overconsolidated alluvial soft/very soft clays, Eu is approximately 250 times Su.

 

[dgillette]

I have to wonder whether you are asking the right question. ponder

This question was cross-posted on two other forums. My response on one of them is shown below. I'm not sure what I was thinking when I wrote "5 kPa" instead of 10 kPa, but 10 kPa ~ 210 psf is still a pretty small number. One of you others might sound off on whether Young's modulus and elastic response is a good way to look at the problem of immediate settlement on that material.


________________________________________
If the strength is only 5 kPa ~ 105 psf, it wouldn't take much of a fill on it to cause slope instability, mud waves, intrusion of individual rocks into the clay, etc. Initial settlement is probably governed much more by shear strain than by vertical compression.

If it really was just vertical compression, the initial settlement (before there is any consolidation due to dissipation of pore pressure) would be quite close to zero, since, if the material is saturated clear through, the compressibility is governed by the bulk modulus of water. There would be some consolidation taking place during the course of fill placement, however.

Can't say much more without knowing details.

 

[fattdad]

To the point of dgillette: Completly agree. If I was constructing a rock embankment on any soft clay, I'd be looking at the preconsolidation pressure, the undrained shear strength, values of Cv and the likely need for wick drains to relieve excess pore pressure allowing an increase of undrained shear strength to accomodate the vertical effective stresses associated with the embankment.

I'd think immediate settlement irrelavent for a soft clay.

To the original post, I did want to attempt a direct answer to your direct question. Your final comment was not posed as a question, so I kind of ignored it. That said, I tend to think you are off track.

f-d

¡papá gordo ain’t no madre flaca!