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Geotechnical workflowCompleted analysis required

Slope-Stability
Factor Comparison

Compare a factor of safety from a completed geotechnical stability analysis with the criterion selected for the exact project condition.

Who it's for: geotechnical and civil engineers checking a completed slope-stability factor of safety at construction documents against the selected project criterion.

Entered-factor comparison
analyzed FS ÷ required FS

How to use this calculator

1
Complete the geotechnical analysis outside this worksheet
Establish the ground and groundwater model, strength basis, loads, geometry, credible failure mechanisms, analysis condition, and appropriate equilibrium method.
2
Select the project criterion
Use the criterion required for the exact condition, consequence, owner, authority, standard, and uncertainty basis—not a generic website threshold.
3
Enter the analyzed factor
Use the governing reviewed result for the same condition and criterion basis.
4
Read the arithmetic comparison
The worksheet returns a ratio and difference only; it does not validate either input or declare a slope stable.

The formula

Comparison ratio = analyzed factor of safety ÷ verified required factor of safety.
Difference = analyzed factor − required factor.
No slope-stability method or geotechnical criterion is calculated.

Worked example

Example
A reviewed long-term analysis returns FS = 1.65 and the project-specific required criterion is 1.50. The ratio is 1.65 ÷ 1.50 = 1.10, with a difference of +0.15. This does not independently validate the ground model, analysis, criterion, or slope performance.

When this estimate will be off

  • Does not construct a ground model or calculate pore pressure, strength, loads, a failure surface, resisting/driving forces, or factor of safety.
  • Does not select an infinite-slope, ordinary/Bishop, Spencer, Morgenstern-Price, finite-element, seismic, probabilistic, or other analysis method.
  • Does not choose an acceptable factor of safety; criteria depend on the project, condition, consequence, authority, uncertainty, and governing requirements.
  • An entered analyzed factor above an entered criterion is not a stability, safety, monitoring, construction, or approval statement.

Frequently asked questions

A common mistake: Does not construct a ground model or calculate pore pressure, strength, loads, a failure surface, resisting/driving forces, or factor of safety.

It addresses only a restricted idealization. The former implementation also defined and applied pore-pressure ratio inconsistently, while the public result implied a general stability verdict.

Use the value established for the exact project and analysis condition by the governing owner, authority, standard, and responsible geotechnical engineer. This worksheet intentionally has no universal default rule.

No. It means only that one entered number is no smaller than another. Model completeness, parameter uncertainty, method suitability, failure mechanisms, construction, monitoring, and professional judgment remain decisive.

Sources

This free Slope Stability Factor of Safety Calculator is built and maintained by DataDrivenAEC, using the relevant codes and standards. It does not substitute for professional judgment.