Skip to main content
Calcimator

Landslide Risk Calculator

Slope stability factor from soil, angle, and water table.

Inputs

Results

Factor of Safety

0.88

Stability (0-3)0
Shear strength (kPa)20.67
Shear stress (kPa)23.38
Critical slope angle (°)26.5
Critical soil depth (m)1.94
How to Use This Calculator
  1. Measure or estimate the Slope angle (°) from topographic data or a clinometer.
  2. Enter Soil thickness (m) above the potential slip surface — from field investigation or auger logs.
  3. Set the Friction angle (°) and Cohesion (kPa) from laboratory shear-strength tests or published soil tables.
  4. Adjust the Saturation ratio (0–1) to represent dry (0), partially saturated (0.5), or fully saturated (1) conditions after heavy rainfall.
  5. Read the Factor of Safety: values above 1.5 indicate stability, 1.0–1.25 are conditionally unstable, and below 1.0 means failure is expected.

How the result changes with Slope angle (°)

Slope angle (°)Factor of Safety
9.82.79
320.83
580.45
800.61

What each input means

Slope angle (°)
Angle of the hillslope from horizontal in degrees.
Soil thickness (m)
Depth of soil above the bedrock or potential slip surface.
Friction angle (°)
Internal friction angle of the soil. Clay ~15-25°, sand ~30-40°, gravel ~35-45°.
Cohesion (kPa)
Effective soil cohesion. Sand/gravel ~0, silty clay ~5-20, stiff clay ~25-50.
Saturation ratio (0-1)
Water table height as fraction of soil thickness. 0=dry, 0.5=half saturated, 1=fully saturated.

What each result means

Factor of Safety
Ratio of resisting to driving forces. Below 1.0 = failure expected, above 1.5 = stable.
Stability (0-3)
0=Unstable (<1.0), 1=Conditionally unstable (1.0-1.25), 2=Marginal (1.25-1.5), 3=Stable (>1.5).
Shear strength (kPa)
Total resisting shear strength along the slip surface.
Shear stress (kPa)
Gravitational driving shear stress along the slip surface.
Critical slope angle (°)
Maximum slope angle before failure occurs with current soil and water conditions.
Critical soil depth (m)
Maximum soil thickness before failure at the current slope angle.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Slope angle (°) = 30, Soil thickness (m) = 3, Friction angle (°) = 28, Cohesion (kPa) = 5 = 5 input(s) provided
  2. Calculate Factor of Safety
    0.884 = 0.884
  3. Calculate Stability
    Stability
    0 = 0
  4. Calculate Shear strength
    20.67 = 20.67

Related Calculators

The questions that sit next to this one — chosen by subject, including calculators filed under a different category.

Earth Science

Karst Feature Calculator

Sinkhole risk from limestone depth and water table.

Earth Science

Earthquake Distance Calculator

Epicenter distance from P-wave and S-wave arrival times.

Civil Engineering

Slope Stability Calculator

Analyze slope stability using the infinite slope method. Calculates factor of safety considering cohesion, friction, pore pressure, and slip depth.

Winter Sports & Skiing

Avalanche Risk Calculator

Estimate avalanche danger rating from slope angle, snowpack stability, recent snowfall, wind loading, and temperature trends. Uses the North American Avalanche Danger Scale.

Earth Science

Volcano Hazard Zone Calculator

Hazard radius from eruption type and VEI.

More in Science & Physics.