1. What is Rip Rap Sizing?

Rip rap is a loose assemblage of large stones used to protect soil from erosion in areas of concentrated flow or wave action. The d50 represents the median stone size where 50% of the stones are larger and 50% are smaller by weight.

2. How Does the Calculator Work?

The calculator uses the Rip Rap Sizing equation:

Where:

• \( d_{50} \) — Median stone size (feet)
• \( v \) — Velocity of water (feet per second)
• \( k \) — Dimensionless stability coefficient (typically 0.69)
• \( g \) — Acceleration due to gravity (32.2 ft/s²)
• \( s \) — Specific gravity of stone (typically 2.65 for rock)

Explanation: The equation calculates the minimum stone size needed to resist displacement by flowing water based on velocity and material properties.

3. Importance of d50 Calculation

Details: Proper rip rap sizing is crucial for effective erosion control. Undersized stones will wash away, while oversized stones are unnecessarily expensive and may create turbulence.

4. Using the Calculator

Tips: Enter velocity in feet per second, use default values for k factor (0.69) and specific gravity (2.65) unless you have specific project requirements. Gravity is fixed at 32.2 ft/s².

5. Frequently Asked Questions (FAQ)

Q1: What is a typical k factor value?
A: The standard value is 0.69 for angular rock. Use 0.79 for rounded rock or 0.89 for very turbulent flow conditions.

Q2: How does specific gravity affect the result?
A: Higher specific gravity (denser rock) allows for smaller stones, while lighter materials require larger sizes.

Q3: What safety factors should be considered?
A: Many designs use a safety factor of 1.2-1.5, multiplying the calculated d50 by this factor.

Q4: Are there limitations to this equation?
A: This method is best for uniform flow conditions. For wave action or very steep slopes, other methods may be more appropriate.

Q5: How should rip rap be installed?
A: Proper installation includes geotextile fabric beneath the stones and placement in multiple layers for stability.