How to Determine the Stability Of Slopes?

To determine the stability of slopes, we first need to identify the type of soil. A cohesive soil behaves differently then Cohesionless Soils

Case 1 – When we have Cohesionless Soils
We consider the slope stable if it satisfies the following condition. Please note we consider no water seepage in this situation
i < f
where
i = slope of ground surface
f = angle of internal friction of soil

When seepage factor is introduced parallel to the slope and we assume that soil is totally saturated, the slope is considered stable if it fulfill this condition

tan i < (Y_b/Y_sat) tan f

Case -2 When we have Cohesive Soils
The slope on a cohesive soil is considered stable if
H < (C/YN)
where
H = height of slope, ft (m)
C = cohesion, lb/ft² or kg / m²
Y = unit weight, lb/ft³ or kg / m³
N = stability number and is dimensionless