1. What is Pore Pressure given Effective Stress?

Definition: This calculator determines the total pore pressure in a soil slice based on the total normal force, length of the arc, and effective normal stress.

Purpose: It helps geotechnical engineers analyze slope stability by calculating pore water pressure which affects the shear strength of soils.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( \Sigma U \) — Total pore pressure (N)
• \( P \) — Total normal force acting at the base of the slice (N)
• \( l \) — Length of arc of the slice (m)
• \( \sigma' \) — Effective normal stress (Pa)

Explanation: The total normal force per unit length minus the effective stress gives the pore pressure.

3. Importance of Pore Pressure Calculation

Details: Accurate pore pressure calculation is critical for slope stability analysis, foundation design, and understanding soil behavior under different loading conditions.

4. Using the Calculator

Tips: Enter the total normal force in Newtons, length of arc in meters, effective normal stress in Pascals, and tolerance percentage. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is effective normal stress?
A: It's the stress carried by the soil skeleton, calculated as total stress minus pore water pressure.

Q2: Why include a tolerance percentage?
A: The tolerance (±5% by default) accounts for measurement uncertainties and material variability.

Q3: What units should I use?
A: Use consistent SI units: Newtons (N) for force, meters (m) for length, and Pascals (Pa) for stress.

Q4: When would pore pressure be negative?
A: Negative pore pressure (suction) can occur in unsaturated soils or during drying conditions.

Q5: How does pore pressure affect slope stability?
A: Higher pore pressures reduce effective stress, decreasing shear strength and potentially causing slope failure.

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