Check factors of safety for real project slopes. Model water, loads, and seismic influences easily. Explore regrading, drains, berms, and reinforcement options fast here.
This calculator estimates a preliminary Factor of Safety (FoS) for slopes using two simplified approaches: an infinite-slope (planar) check for shallow failures and a Bishop simplified circular slip search for deeper rotational failures. It helps you compare scenarios and test common mitigation ideas before detailed design.
Many projects use target FoS values around 1.30 for long-term static conditions and about 1.10 for pseudo-static seismic screening. Your required target depends on codes, consequence class, groundwater uncertainty, and construction staging. Always align the target with the governing standard and site risk.
Enter layers to reflect changing materials with depth. For drained behavior, cohesion (c) and friction angle (φ) represent effective-stress strength. For short-term undrained behavior, use Su and the calculator assumes φ ≈ 0. Select the governing layer that best represents the likely failure zone.
Water commonly controls stability. This calculator uses the pore-pressure ratio ru to approximate pore pressure effects. Typical screening values may range from about 0.05 in dry conditions to 0.35 for saturated slopes, rising to 0.50–0.60 during prolonged rainfall or rapid drawdown. Use “Custom” to match site-specific assumptions.
Crest surcharge (q) represents stockpiles, traffic, or structures near the crest. Increasing q generally increases driving demand and can reduce FoS. The seismic coefficient kh provides a pseudo-static screening effect by increasing driving shear. Use conservative values when site data and seismic hazard are uncertain.
The results panel summarizes several quick “what-if” actions: regrading to a flatter slope angle, reducing ru as a proxy for drainage improvement, adding a toe berm/buttress, and adding reinforcement (soil nails, anchors, or geogrid layers). The tool reports the approximate change in FoS and a simple reinforcement spacing estimate per meter width.
Sensitivity results show how FoS changes when φ varies by ±2 degrees, c varies by ±10%, and ru shifts by ±0.10. If FoS is highly sensitive to ru, prioritize drainage details, water control, and seasonal groundwater assumptions. If FoS is sensitive to φ or c, refine lab/field strength data and stratigraphy.
Use this tool for early screening and option comparison, then validate using detailed seepage analysis, non-circular mechanisms (where applicable), staged construction effects, and method selection appropriate for your material and geometry. Final designs should include global stability, internal stability for reinforcement systems, facing/drainage details, and construction QA/QC.
Use infinite-slope for shallow, planar failures in uniform materials. Use Bishop circular mode for rotational failures where depth is significant. When unsure, run both and treat the lower FoS as the conservative screen.
ru is a pore-pressure ratio used to approximate pore water pressure effects without full seepage modeling. Higher ru typically means more pore pressure, lower effective stress, and a lower FoS. Use site data where possible.
Select “Rainfall” or “Rapid drawdown” to apply higher default ru values, then refine with “Custom” if you have field piezometers or seepage results. These cases often govern and deserve conservative assumptions.
Yes. Set a layer to undrained and enter Su. The calculator uses Su as cohesion and sets φ to approximately zero. This is useful for short-term construction conditions in saturated clays.
The tool computes the additional resisting demand to reach the target FoS in the planar check, then divides by a reduced element capacity and a conservative inclination effectiveness. It is a screening estimate, not a final structural design.
The grid search is intentionally modest for speed and may miss some geometries. Adjust geometry inputs, ensure H and β are realistic, and try again. For complex slopes, use professional software with robust search methods.
No. This is a preliminary calculator for screening and option comparison. Final design typically requires detailed geotechnical investigation, seepage modeling, appropriate design standards, and engineered detailing for stabilization measures.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.