Slope Stability Factor of Safety Calculator
Calculate the factor of safety for slope stability using the infinite slope method.
Includes groundwater effects.
Factor of Safety
Infinite Slope Method FS = (c + (γ·z·cos²β − u) × tan φ) / (γ·z·sin β·cos β)
Where c = cohesion (kPa), γ = unit weight (kN/m³), z = depth to failure plane (m), β = slope angle (°), φ = friction angle (°), u = pore water pressure (kPa).
Pore Water Pressure For a dry slope: u = 0. For a fully saturated slope (water table at surface): u = γw × z (where γw = 9.81 kN/m³).
Interpretation FS < 1.0: Failure likely. FS 1.0–1.25: Marginally stable. FS 1.25–1.5: Adequate stability. FS > 1.5: Stable.