HumayunKabir,

The natural moisture content of the sample will, in addition to the properties mentioned by you, exert a significant effect on the results of the UCS test.

The failure plane (assuming that the failure occurs with a well-defined shear failure plane) would seem to me to be difficult to measure accurately, and may be influenced by any number of things, such as (for example) the random presence of granular-sized particles within the cohesive matrix.

I would think that there would not be any plausible relationship between the UCS shear angle and the (I am assuming) critical slope angle for backfill, as the soil tested in the lab would be in a much different state of stress than that in an embankment.

Jeff

Jeffrey T. Donville, PE
TTL Associates, Inc.
www.ttlassoc.com

The views or opinions expressed by me are my own and do not necessarily reflect the views or opinions of my employer.

The internal angle of friction for cohesionless soils is the natural angle of a stable slope with the same angle and same soils, in theory at least.

Suggest you look up Lambe and Whitman's book - they explain very nicely "failure" plane orientation vs side slope (I take this as the safe slope considering overall stability).  For you to determine the "friction angle" and I put this is parenthesis because there are a number of them, you would need to test your soil at several confining pressures in order to get one.  You need, too, to be cognizant of the fact that if your sample that is tested is "natural", then it will behave different that the same material used in a fill - the later being affected by the compacted density (and how well the material kneads together - clayey soils).  You can refer to Bishop's paper in the 1960 ASCE Boulder Conference on Clay Soils.

Thanks