Slope stability refers to the condition of inclined soil or rock slopes to withstand or undergo movement. Similarly, a Stability Of Slopes can be locally stable if a safety factor larger than 1 is computed along any potential sliding surface running through a limited portion of the slope we study about Failure of Slopes, Factor of safety
- Slopes⇒ A soil mass, when the elevation of the ground surface gradually changes.
- Natural Slopes⇒ Mountains, Hilly Areas, Snow-covered mountains.
- Man-Made Slopes⇒ Slopes of embankments for roads, railway lines, Canals, etc
- Infinite Slopes⇒ Constant slopes for infinite extent (Mountains)
- Finite Slopes⇒ Slopes that are finite in extent like Gravity dam, Embankments, etc
Causes of Failure of Slopes
Gravitational Forces⇒ The soil mass bounded by a slope has a tendency to slide down due to self-weight
Force due to seepage of water, Erosion of the surface of slope due to flowing water
A sudden lowering of water adjacent to a slope, Earthquake Force.
Factor of Safety
The factor of safety is commonly thought of as the ratio of the maximum load or stress that a soil can sustain to the actual load or stress that is applied. Referring to Fig. 11.1 the factor of safety F, with respect to strength,
naturally, an entire industry has cropped up around the need to manufacture safe products and structures for consumer use.
Most commonly, you’ll hear the terms “Factor of Safety” (FoS) or “Safety Factor (SF), but there are several definitions and calculations that may be referred to. Let’s look at the basics of FoS for design and engineering.
Good design engineers must consider so many factors when designing a part or component.
- Factor of safety w.r.t shearing strength
- The factor of safety with respect to cohesion may be defined as the ratio between the actual cohesion and the cohesion required for stability when the frictional component of strength is fully mobilized cohesion.
- The factor of safety with respect to friction may be defined as the ratio of the tangent of the angle of shearing resistance of the soil to the tangent of the mobilized angle of shearing resistance of the soil when the cohesive component of strength is fully mobilized.
Factor of Safety” usually refers to one of two things: 1) the actual load-bearing capacity of a structure or component, or 2) the required margin of safety for a structure or component according to code, law, or design requirements.
A very basic equation to calculate FoS is to divide the ultimate (or maximum) stress by the typical (or working) stress.
A FoS of 1 means that a structure or component will fail exactly when it reaches the design load, and cannot support any additional load. Structures or components with FoS < 1 are not viable; basically, 1 is the minimum. With the equation above, an FoS of 2 means that a component will fail at twice
- Stability Analysis of Infinite Slope in Sand (Cohesionless Soil)⇒
- Stability Analysis of Infinite Slope in Clay (Cohesive Soil)
- Up to, line OA never intercepts the line ‘FA’, and the slope is stable for any value of depth.
- If, line OA will intercept the line ‘FA’ at A. Slope is safe even if it is steeper than, as long as the depth of the slope is such that shear stress is less than stress strength.
- If then at a particular depth the shear stress will be equal to shear strength (factor of safety=1) and that depth is known as critical depth.