Effective Cohesion of Soil given Normal Stress on Slice Calculator

Effective Cohesion Formula:

\[ c' = \tau - ((\sigma_{normal} - u) \times \tan(\phi' \times \frac{\pi}{180})) \]

Shear Strength of Soil (τ):

Normal Stress (σ):

Upward Force (u):

Effective Angle of Internal Friction (φ'):

Effective Cohesion (c'):

1. What is Effective Cohesion of Soil?

Definition: Effective cohesion is the shear strength of soil when normal stress is zero, representing the inherent bonding between soil particles.

Purpose: It's a critical parameter in geotechnical engineering for slope stability analysis and foundation design.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ c' = \tau - ((\sigma_{normal} - u) \times \tan(\phi')) \]

Where:

\( c' \) — Effective cohesion (Pa)
\( \tau \) — Shear strength of soil (Pa)
\( \sigma_{normal} \) — Normal stress on slice (Pa)
\( u \) — Upward force due to pore water pressure (Pa)
\( \phi' \) — Effective angle of internal friction (degrees)

Explanation: The formula calculates cohesion by subtracting the frictional component from the total shear strength.

3. Importance of Effective Cohesion

Details: Accurate cohesion values are essential for predicting soil behavior under stress and designing stable earth structures.

4. Using the Calculator

Tips: Enter all parameters in Pascals (Pa) and the friction angle in degrees. The friction angle typically ranges between 0° and 45°.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between total and effective cohesion?
A: Total cohesion includes pore water pressure effects, while effective cohesion considers only the soil skeleton strength.

Q2: How do I measure shear strength of soil?
A: Shear strength is typically determined through laboratory tests like direct shear or triaxial tests.

Q3: What affects the effective angle of internal friction?
A: Soil type, density, particle shape, and stress history all influence the friction angle.

Q4: Can cohesion be negative?
A: No, cohesion is always positive or zero. Negative values indicate calculation errors.

Q5: How does pore water pressure affect cohesion?
A: Higher pore pressure reduces effective stress, which can decrease the apparent cohesion.