About the Slope Stability Calculator
This tool calculates the Factor of Safety (FoS) for slopes using various methods of analysis. The FoS is defined as the ratio of resisting forces to driving forces along a potential failure surface.
Factor of Safety Interpretation
- FoS < 1.0: Slope is unstable and likely to fail
- 1.0 ≤ FoS < 1.3: Marginally stable (may be acceptable for temporary slopes)
- 1.3 ≤ FoS < 1.5: Conditionally stable (may require monitoring)
- FoS ≥ 1.5: Generally considered stable for permanent slopes
Available Analysis Methods
The simplest limit equilibrium method that assumes the resultant of interslice forces is parallel to the base of each slice. It tends to be conservative (underestimates FoS).
Formula: FoS = Σ(c·l + N·tanφ) / ΣW·sinα
An improved method that satisfies vertical force equilibrium and assumes horizontal interslice forces are equal. More accurate than Fellenius for circular slip surfaces.
Suitable for non-circular slip surfaces. Satisfies horizontal and vertical force equilibrium but not moment equilibrium.
Provides quick estimates of FoS using dimensionless stability numbers for homogeneous slopes with simple geometry.
Understanding the Results
The calculator provides several outputs to help assess slope stability:
- Factor of Safety: Primary indicator of stability
- Critical Slip Surface: Location and geometry of the most likely failure surface
- Visualizations: Diagrams showing the slope geometry and failure mechanism
- Analysis Details: Information about the method used and assumptions made
Limitations
- Simplified 2D analysis (plane strain conditions)
- Does not account for progressive failure
- Assumes homogeneous soil properties
- Does not consider tension cracks or reinforcement
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