Slope Stability Calculator (Infinite Slope)

Slope Stability Calculator (Infinite Slope) | Online Free Tool | Elysia Tools

Tool usage guide

Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Category: Math & Numbers
Input types: select, number
Output type: json
Sample coverage: 4
API ready: Yes

Overview

The Slope Stability Calculator (Infinite Slope) computes the factor of safety (FS) for translational slope failures using the infinite-slope model. It supports both dry slopes and conditions with seepage parallel to the slope face, outputting the calculated FS alongside a stability classification of stable, marginal, or unstable.

When to use

When analyzing shallow, translational landslide hazards where the failure surface is parallel to the ground surface.
When evaluating the impact of groundwater seepage parallel to a slope face on soil shear strength and stability.
When performing preliminary geotechnical assessments of long, uniform slopes in civil engineering and geological hazard planning.

How it works

1Select the calculation mode, choosing between a dry slope (no seepage) or a slope with seepage parallel to the surface.
2Input the soil parameters including effective cohesion (c'), effective friction angle (φ'), slip depth (z), and soil unit weight (γ or γ_sat).
3Enter the slope angle (β) and, if in seepage mode, the unit weight of water (γ_w).
4Run the calculator to compute the driving shear stress, cohesion and friction contributions, and the final factor of safety (FS) with its stability classification.

Use cases

Assessing the stability of long, uniform sandy slopes under dry conditions.
Estimating the reduction in safety factor for a hillside during heavy rainfall that causes parallel seepage.
Verifying manual geotechnical calculations for infinite slope stability homework or design checks.

Examples

1. Dry Sandy Clay Slope Assessment

Geotechnical Engineer

Background

An engineer needs to evaluate a dry, uniform slope with a 30-degree incline to determine if a shallow slip plane at 3 meters depth is stable.

Problem

Calculate the factor of safety for a dry slope with cohesion of 10 kPa, friction angle of 25 degrees, and soil unit weight of 18 kN/m³.

How to use

Select 'Dry' mode, enter 10 for Effective Cohesion, 25 for Effective Friction, 30 for Slope Angle, 3 for Slip Depth, and 18 for Soil Unit Weight.

Outcome

The calculator outputs a factor of safety of 1.2353, classifying the slope stability as marginal.

2. Saturated Slope with Parallel Seepage

Civil Engineering Consultant

Background

A consultant is assessing a hillside prone to heavy rainfall where water flows parallel to the slope face, potentially triggering a landslide.

Problem

Determine the factor of safety at a 3-meter slip depth for a 30-degree slope with a saturated unit weight of 20 kN/m³, cohesion of 5 kPa, and friction angle of 25 degrees.

How to use

Select 'Seepage parallel to slope' mode, enter 5 for Effective Cohesion, 25 for Effective Friction, 30 for Slope Angle, 3 for Slip Depth, 20 for Saturated Unit Weight, and 9.81 for Water Unit Weight.

FAQ

What is the difference between the dry and parallel seepage modes?

Dry mode assumes no water table, while parallel seepage mode assumes groundwater is flowing parallel to the slope face, reducing effective stress using the saturated unit weight and water unit weight.

How is the stability classification determined?

A factor of safety (FS) less than 1 is classified as unstable, between 1 and 1.5 is marginal, and 1.5 or greater is stable.

Can I use this calculator for deep, circular slope failures?

No, this calculator is specifically designed for infinite slopes where failure occurs along a shallow plane parallel to the slope surface.

What value should I use for effective cohesion in cohesionless soils?

For clean sand or gravel with no cohesion, set the effective cohesion (c') to 0.

What is the default unit weight of water used in the calculations?

The default unit weight of water (γ_w) is 9.81 kN/m³, but you can adjust this value if needed.

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Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Overview

When to use

How it works

Use cases

Examples

1. Dry Sandy Clay Slope Assessment

2. Saturated Slope with Parallel Seepage

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