Slope stability using the method of slices

What the tool calculates

• Circular slip surface search using entry and exit points and circle position
• Minimum factor of safety from NBR 11682:2009, based on the selected levels of protection for life and against damage
• Groundwater level for unit weights, ru for pore pressure, and seismic coefficients kh/kv
• Reference values for typical soils, with source identification and review by the designer

What you enter

• Slope geometry and soil profile
• Average soil strength parameters and unit weight: c, φ and γ
• Levels of protection for life and against damage

What you receive

• Lowest factor of safety found among valid candidates and its corresponding slip surface
• Comparison with the adopted minimum factor of safety
• Result accounting for the specified water and seismic conditions

References and limits of applicability

• ABNT NBR 11682:2009 — Slope stability (Table 3, minimum factor of safety by safety level)

Checks and considerations

• Factor of safety below the minimum adopted for the selected safety levels
• The high test variability option increases the minimum factor of safety by 10%

How it works

Fellenius and simplified Bishop assess slice equilibrium along circular slip surfaces. This tool uses average soil parameters, without independent strength values for each layer. Groundwater level affects weights, while ru represents pore pressure. The lowest factor found depends on the search domain and discretisation; it does not guarantee the absolute minimum for the slope.

Example of use

To study a cut slope, enter its geometry and representative soil parameters. Compare the applicable water conditions and examine the identified slip surface and adopted minimum factor of safety. If stratification controls failure, assess the need for a model that represents the layers explicitly.

Frequently asked questions

Does the tool account for variability in test results?

A high test variability option increases the adopted minimum factor of safety by 10%, with reference to NBR 11682:2009. The responsible professional must assess whether this condition applies to the project.

Generated documents

These documents are assembled within your project using data from the corresponding tools.

• Geotechnical calculation report — Combine calculation reports for soil stress bulbs, retaining walls, reinforced soil walls, slope stability and soil-nailed slopes in one PDF. The document consolidates saved calculations without repeating or cross-checking the individual tools' verifications.