2012-10-01_REVISION - M1977306 ‎(17)‎

• Permit No: M1977306
• IBM Index Class Name: REVISION
• Doc Date: 10/1/2012
• Doc Name: EPP Submittal- Ex. 6.5 to Material Safety Data
• From: Cotter
• To: DRMS
• Type & Sequence: AM1
• Media Type: D
• Archive: No

Factor of Safety (FS)
For infinite slopes consisting of cohesionless soils that are either above the water table or
that are fully submerged, the factor of safety for slope stability is determined as follows:
FS = Tancp /Tan13
where
cp = the angle of internal friction for the soil
(3 = the slope angle relative to the horizontal
(WSDOT Geotechnical Design Manual M)
There could be a small amount of cohesion which would add to the strength but this will
be ignored in order to calculate the worst case scenario.
FS = tan (40 °) /tan (26.56 °) = 1.67
>1.4 is the recommended parameter for safety factor of permanent slopes.
Thus the 2:1 slope satisfies the Factor of Safety for this material.