How do you saturate soil specimens 4

[roadrunner13]

How do you saturate soil specimens for UU triaxial testing or UCS? Assuming they are partially saturated.

"There is nothing in the desert, and no man needs nothing."

 

[EireChch]

saturation is via back pressure in triaxial cell. Your skepmpton B parameter should be greater than 95% to be considered fully saturated.

However, UUs are often not saturated using back pressure. Test is just ran at the current moisture content, which is likely below fully saturated. For samples above the water table, the saturation level is obviously further from 95% saturated.

The affect of samples not being at least 95% saturated is that you will get some phi and cohesion. It seems that the industry has just accepted this. Its similar to doing vane shear or pocket penetrometer tests to get undrained shear strength. Test is undertaken at its existing moisture content.

UCS tests are never saturated.

 

[roadrunner13]

Ok. That "some phi" (in totals), What is it used for in calculations? You are supposed to check undrained conditions with Su and phi = 0º, and drained conditions with c' and phi'.

"There is nothing in the desert, and no man needs nothing."
CEDEX Madrid graduate.

 

[EireChch]

yes, Cu for undrained and c' phi' for drained.

Dont use any phi you get from an undrained test, it is just down to poor saturation (in most cases).