Hi
Its depend on the type of slope you r analyzing. Let me know type of slope and conditions please.
Meantime see following paper if you fin it interest.
https://www.academia.edu/9805623/A_new_geotechnical_method_for_natural_slope_exploration.
Thanks.
SPECIFIC GRAVITY IS NOT ALWAYS BETWEEN 2.6 TO2.8 . IT MAY VARY ACCORDING TO THE PARTICLE SIZE. IT MAY BE 2.4, 2.45, 2.5 2.6, 2.65.....HOWEVER VERY ACCURATE VALUE OF SPECIFIC GRAVITY NEEDS FOR LOT OF GEOTECHNICAL CALCOLATIONS. SO SUCH RESULTS CAN BE VARY IF THE SECOND DECIMAL OF SPECIFIC GRAVITY...