1. What is Effective Normal Stress in Soil Mechanics?

Definition: Effective normal stress is the stress carried by the soil skeleton, calculated by subtracting pore water pressure from total normal stress.

Purpose: It's crucial for analyzing soil strength, stability, and deformation characteristics in geotechnical engineering.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( \sigma' \) — Effective normal stress (Pa)
• \( \sigma_n \) — Total normal stress (Pa)
• \( F_u \) — Upward force due to seepage (Pa)

Explanation: The upward seepage force reduces the effective stress in the soil, which is critical for stability analysis.

3. Importance of Effective Stress Calculation

Details: Proper calculation helps prevent failures like piping, heaving, or liquefaction in soils subject to seepage forces.

4. Using the Calculator

Tips: Enter the total normal stress, upward seepage force, and safety factor (±5%). All values must be ≥ 0.

5. Frequently Asked Questions (FAQ)

Q1: What is the upward seepage force?
A: It's the pore water pressure acting upward against the soil particles, reducing the effective stress.

Q2: Why include a safety factor?
A: The ±5% safety factor accounts for uncertainties in measurements and variable field conditions.

Q3: What units should I use?
A: The calculator uses Pascals (Pa), but you can enter kN/m² values as they're equivalent to kPa.

Q4: What if my upward force exceeds normal stress?
A: This indicates potential heaving or boiling conditions where effective stress becomes zero or negative.

Q5: How is this different from total stress?
A: Total stress includes both soil skeleton stress and pore water pressure, while effective stress only considers the soil skeleton.

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