Using the simplified Janbu method, determine the factor of safety for stability of a slope and potential failure mass identified by the following description: • Slope inclination is 30°; surface is...

Using the simplified Janbu method, determine the factor of safety for stability of a slope and potential failure mass identified by the following description:

• Slope inclination is 30°; surface is level at top of slope.

• Slope height is 20 m; soil unit weight γ is 17 kN/m³.

• Buried thin weak layer (the assumed plane of sliding) extends back from toe of slope at an inclination of 20° for a horizontal distance of

40 m, then upward at a 45° inclination until it intersects the ground surface (c = 12 kN/ m², y = 17 kN>m³
, ɸ= 18° ).