Angle of internal friction vs water content of soil

[ketanco]

How is the angle of internal friction related to the water content of the soil?

And when we perform triaxial tests, the UU, CD, CU type tests, they are normally for saturated samples correct? or any moisture content is possible?

 

[civilrobot]

I'm in the middle of studying this now and I think I can give some sort of input to your first question. 

Rankine Active Pressure Coefficient, Ka=(1-sin (angle of internal friction))/(1+sin (angle of internal friction))

total stress = Ka*moist unit weight*height from ground surface to point of interest

moist unit weight= [(degree of saturation*void ratio+specific gravity)* unit weight of water]/(1 + void ratio)

water content = (degree of saturation*void ratio)/specific gravity

This looks so much better with the actual symbols but this is the connection that stood out to me.

ETA: So it seems that the pressure exerted by the water is part of the stress put on the soil particles which adds to the overall active pressure on a particular barrier like a retaining wall or on some other object.