Effective Cohesion of Soil given Shear Force in Bishop's Analysis Calculator

Effective Cohesion Formula:

\[ c' = \frac{(S \times fs) - ((P - (u \times l)) \times \tan(\phi' \times \frac{\pi}{180}))}{l} \]

Shear Force on Slice (S):

Factor of Safety (fs):

Total Normal Force (P):

Upward Force (u):

Length of Arc (l):

Effective Angle of Internal Friction (φ'):

Effective Cohesion (c'): Pa

1. What is Effective Cohesion in Bishop's Analysis?

Definition: Effective cohesion is the shear strength of soil that is independent of interparticle friction, calculated using Bishop's simplified method of slices.

Purpose: This calculation is essential for slope stability analysis in geotechnical engineering.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ c' = \frac{(S \times fs) - ((P - (u \times l)) \times \tan(\phi' \times \frac{\pi}{180}))}{l} \]

Where:

\( c' \) — Effective cohesion (Pa)
\( S \) — Shear force on slice (N)
\( fs \) — Factor of safety (±5%)
\( P \) — Total normal force (N)
\( u \) — Upward force due to pore water pressure (Pa)
\( l \) — Length of slice base (m)
\( \phi' \) — Effective angle of internal friction (°)

3. Importance of Effective Cohesion Calculation

Details: Accurate calculation of effective cohesion is critical for assessing slope stability and preventing landslides.

4. Using the Calculator

Tips: Enter all required parameters. The factor of safety typically ranges from 1.3 to 1.5 (±5% variation). Angle of internal friction is in degrees.

5. Frequently Asked Questions (FAQ)

Q1: What is Bishop's method of analysis?
A: A simplified method for slope stability analysis that considers interslice forces but assumes they are horizontal.

Q2: Why is pore water pressure important?
A: It reduces effective stress in soil, decreasing shear strength and slope stability.

Q3: What's a typical factor of safety range?
A: Usually 1.3-1.5 for slopes, with ±5% acceptable variation in calculations.

Q4: How does cohesion affect slope stability?
A: Higher cohesion increases soil shear strength, improving slope stability.

Q5: What units should I use?
A: Use consistent SI units: Newtons (N) for forces, Pascals (Pa) for pressures, meters (m) for lengths.