Stability Number for Cohesive Soil Calculator

Stability Number Formula:

\[ S_n = \frac{c}{\gamma \times h_{cs}} \]

Cohesion of Soil:

kPa

Unit Weight of Soil:

kN/m³

Critical Depth:

Safety Factor (±5%):

Stability Number (S_n):

Adjusted Value (±5%):

1. What is Stability Number for Cohesive Soil?

Definition: The Stability Number is a dimensionless parameter used to assess the stability of slopes in cohesive soils.

Purpose: It helps geotechnical engineers evaluate slope stability and predict potential failures in cohesive soil masses.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ S_n = \frac{c}{\gamma \times h_{cs}} \]

Where:

\( S_n \) — Stability Number (dimensionless)
\( c \) — Cohesion of soil (kPa)
\( \gamma \) — Unit weight of soil (kN/m³)
\( h_{cs} \) — Critical depth for stability number (m)

Explanation: The cohesion is divided by the product of unit weight and critical depth to obtain the stability number.

3. Importance of Stability Number

Details: A higher stability number indicates greater slope stability. Values below certain thresholds may indicate potential slope failure.

4. Using the Calculator

Tips: Enter the soil cohesion in kPa, unit weight in kN/m³ (default 18), critical depth in meters (default 0.069), and safety factor in % (default 5%). All values must be ≥ 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical Stability Number range?
A: For stable slopes, S_n typically ranges from 0.1 to 0.3, but this varies with soil conditions.

Q2: How do I determine soil cohesion?
A: Cohesion is determined through laboratory tests like unconfined compression tests or field vane shear tests.

Q3: What does the safety factor represent?
A: The safety factor (±5%) provides a conservative estimate by reducing the calculated value to account for uncertainties.

Q4: How is critical depth determined?
A: Critical depth depends on slope geometry and soil properties, often determined through stability analysis.

Q5: Can this be used for non-cohesive soils?
A: No, this formula is specifically for cohesive soils. Different approaches are needed for granular materials.