The minimum allowable depth of cover is the largest of:
For roads H=B/8+0.2(m) H=B/6(m) and not less than 0.6（m）
For railways H=B/4 and not less than 0.6(m)
Galvanized Steel is the standard finish for all Corrugated Steel Pipe (CSP) and performs well in low-abrasion conditions.
The minimum allowable depth of cover is the largest of:
For roads H=B/8+0.2(m) H=B/6(m) and not less than 0.6（m）
For railways H=B/4 and not less than 0.6(m)
There is a possibility to reduce depth of cover provided that suitable checking calculations will be made.
| Flexible structure | Plate thickness | Kinds of standard corrosion protection | Required average min value(um） |
| plates | ≧6mm | Hot zinc galvanizing | 85 |
| ≧3mm do < 6mm | Hot zinc galvanizing | 70 | |
| ≧1.5mm do < 3mm | Hot zinc galvanizing | 55 | |
| Bolts and nuts | - | Hot zinc galvanizing | 45 |
Highway Construction 
Mine Projection 
Municipal Engineering 
Irrigation Engineering 
Railway Construction Projection 
Other Application 
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