Infinite Slope Stability Seepage Calculator
Geotechnical engineering & hillslope hydrology: Evaluate Factor of Safety ($FS$) against shallow planar translational landslides with steady seepage parallel to the slope face.
Hillslope Geometry & Phreatic Surface
Inclination of mountain / hill slope
Depth to impermeable slip surface / bedrock
Water table height above slip plane (h_w ≤ H)
Root cohesion or soil apparent cohesion
Internal angle of friction
Water unit weight γ_w = 9.81 kN/m³
Infinite Slope Seepage Equation
For planar translational slip surfaces parallel to the ground surface with seepage parallel to the slope:
$$FS = \frac{c'}{\bar{\gamma} H \sin \beta \cos \beta} + \left( 1 - \frac{\gamma_w h_w}{\bar{\gamma} H} \right) \frac{\tan \phi'}{\tan \beta}$$
Notice that when cohesionless soil is fully submerged with surface seepage ($h_w = H, c' = 0$), $FS \approx \frac{1}{2} \frac{\tan \phi'}{\tan \beta}$, cutting stability in half!
Factor of Safety & Limit State
Current Factor of Safety (FS)
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Dry Slope FS (No Seepage)
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Critical Stability Thresholds
Critical Failure Slope Angle
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Angle at which FS = 1.0
Critical Water Height (h_w,crit)
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Water level triggering failure
Landslide Risk Assessment
Cohesion Contribution to FS:
Friction Contribution to FS:
Hillslope Landslide Vulnerability:
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