Soil properties

[mitsiou]

Hi everyone

Could somebody please help me out in defining the following:
Submerged density
Drained and undrained stress
and where are they used?

 

[dirtsqueezer]

I believe undrained stress is just what it says. Below and above the water table. Submerged density is probably how heavy the soil and water are together, ususally per cubic foot. So that would be something like:

[Weight of soil + Weight of water(density of water at a certain temperature/volume of voids)]/volume of soil and voids

That's all from Soil Mechanics and Engineering Practice, Terzaghi and Peck; an old book but I believe the basics are still good.

 

[dgillette]

"Submerged density" might also refer to what's more often called "submerged unit weight" or "bouyant unit weight," which is the total weight of the material (including solids and pore water) minus the unit weight of water. This is what a cubic foot would weigh if it and the scale were under water.

"Drained" and "undrained stress" are also terms that don't quite fit conventional usage, and out of context, their meanings aren't obvious to me. I'd guess they mean "effective stress" and "total stress." Effective stress is the unifying concept of soil mechanics. It governs shear strength, compressibility, elastic properties, etc. You should probably find an undergrad soil-mechanics text.

Bon chance!
DRG

 

[jartgo]

In following to what dgillette was starting, two theories are commonly used to estimate the shear strength of a soil depending on the rate (how fast the load is applied) of shearing. These are the Tresca theory for short term loading of a soil (commonly referred to as the undrained strength or the total stress condition) and Mohr–Coulomb theory, combined with the principle of effective stress, for the long term loading of a soil, commonly referred to as the drained strength or the effective stress condition.

recalling that effective stress is total stress minus pore water pressure.

My disclaimer is that I'm not a geotechnical engineer so I stand to be corrected, I just dug out my text book when I read this post because the terms sounded familiar, but I couldn't remember either.