Pore Pressure Ratio given Unit Weight Calculator

Pore Pressure Ratio Formula:

\[ r_u = \frac{F_u}{\gamma \times z} \]

Pore Pressure Ratio:

1. What is Pore Pressure Ratio?

Definition: Pore pressure ratio is a crude way of describing pore-water conditions in a slope stability analysis.

Purpose: It helps geotechnical engineers assess the effect of water pressure on slope stability.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ r_u = \frac{F_u}{\gamma \times z} \]

Where:

\( r_u \) — Pore pressure ratio (expressed as percentage)
\( F_u \) — Upward force due to seepage water (Pascals)
\( \gamma \) — Unit weight of soil (N/m³)
\( z \) — Height of slice (meters)

Explanation: The upward seepage force is divided by the product of soil unit weight and slice height to determine the pore pressure ratio.

3. Importance of Pore Pressure Ratio

Details: Proper calculation of pore pressure ratio is crucial for slope stability analysis, as it directly affects the shear strength of soil.

4. Using the Calculator

Tips: Enter the upward force in Pascals, unit weight of soil (default 18000 N/m³), and height of slice (default 3 m). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical range for pore pressure ratio?
A: Pore pressure ratio typically ranges from 0 (dry soil) to 1 (fully saturated), often expressed as 0-100%.

Q2: How does pore pressure affect slope stability?
A: Higher pore pressure reduces effective stress in the soil, decreasing shear strength and potentially causing slope failure.

Q3: When would pore pressure ratio be highest?
A: During or immediately after heavy rainfall when soils are saturated and water tables are high.

Q4: What's the relationship between ru and factor of safety?
A: Generally, as ru increases, the factor of safety against slope failure decreases.

Q5: How accurate is this simplified calculation?
A: This provides a rough estimate; detailed analysis requires more sophisticated pore pressure measurements.