What is Ring Stiffness (SN)?
SN (Stiffness Number) represents a pipe's resistance to external loads. A higher SN value means the pipe is stiffer with greater load-bearing capacity. SN4 and SN8 classes are standard for corrugated pipes.
When is SN4 Sufficient?
- Areas without vehicle traffic (park, garden, field)
- Laying depths of 0–3 metres
- Firm, stable soil conditions
- Areas with low groundwater risk
When is SN8 Required?
- Roadsides and areas with vehicle traffic
- Laying depths of 3–6 metres
- Medium or loose soil conditions
- Areas with groundwater present
How to Calculate?
Simplified method: K = (depth × 1.2) + (traffic factor × 0.8) + soil factor. If K < 1.5, SN4 is recommended; if K > 1.5, SN8 is recommended.
Important: This calculation is indicative only. For major projects, always obtain a soil survey and engineer approval.