About Rip Rap and Erosion Control
**Rip rap** (also known as **rock armour** or **shot rock**) is a permanent layer of large, angular stones placed along shorelines, riverbanks, and slopes to protect against water-induced erosion. Its effectiveness relies on the rock's size, angularity (which aids interlocking), density, and layer thickness.
Rip Rap Calculation Formula
The quantity is calculated using volume and density, typically including a waste factor for proper coverage and embedding:
- **Volume ($\text{m}^3$)** = Area $\times$ Thickness
- **Weight (kg)** = Volume $\times$ Density ($\text{kg}/\text{m}^3$)
- **Total Order (Tons/tonnes)** = Weight (Tons/tonnes) $\times$ **1.10** (for 10% Waste Factor)
- **Cost (₹)** = Total Order (Tons/tonnes) $\times$ Price (₹/tonnes)
Typical Rock Densities for Rip Rap
The density used is the solid rock density. Always confirm this value and the required stone size with your project engineer.
| Stone Type | Density ($\text{kg}/\text{m}^3$) | Density ($\text{lb}/\text{ft}^3$) |
|---|---|---|
| Granite | 2600–2700 | 162–168 |
| Limestone | 2400–2600 | 150–162 |
| Basalt | 2800–3000 | 175–187 |
| Sandstone | 2200–2400 | 137–150 |
| Fieldstone | 2600–2650 | 162–165 |
Rip rap is most effective when placed at a thickness of **1.5 times the average rock diameter**. Common sizes range from 4 to 24 inches for different flow and wave conditions.