Hi there

I think, it does not matter what is the percentage of fines you have in your soil. i.e coarse sand can be considered unsaturated if its degree of saturation is between 0 and 100%. But in this case the capillarity of sand is very small. For such kind of soils, degree of saturation decreases rapidly when a small amount of suction is applied that is exceeding the air entry suction. This is because of its high coefficient of permeability. 

I think since you have slope stability analysis, you need to select a soil with a high percentage of fines for more stable analysis. Numerically, you can suggest different percentages of fines 10%, 15%...etc, however, you need to be aware of the suction range. In other words, the capillarity of a soil increases with the fines percentage. The advantage of this may be in that you can extend your soil water characteristic curve (SWCC) so that you can reach the residual suction by applying several hundred kPa of suction rather than just a few kPa when you have coarse sand or gravel. And such higher values of suction may give you the more stable slope. 

Regards

Dear Bestun Shwan sir,

Thank you for your suggestion. I will consider your suggestion while carrying out slope stability analysis.

Hi Adarsh

I agree with Bestun. It also depends on what sort of lab tests you are doing.

Best regards

Ravi

Thank you for the suggestion sir