The main perforation requirements usually include:
Perforation type: circular holes or slots
Hole diameter: commonly 5–10 mm for small-diameter pipes
Hole spacing: evenly distributed along the pipe circumference and length
Perforation arrangement: Class I (partial perforation) or Class II (full perforation)
Water inlet area: minimum opening area per meter must meet drainage standards
Hole location: typically positioned in the corrugation valleys for corrugated HDPE pipes
Edge quality: holes must be cleanly cut without restricting water inflow
For example, under AASHTO Class II standards, the minimum water inlet area is generally:
20 cm²/m for DN100–250 pipes
30 cm²/m for DN300–450 pipes
40 cm²/m for DN600 and larger pipes
In practical engineering, perforation design is also adjusted according to:
groundwater flow rate,
soil particle size,
anti-clogging requirements,
and filter fabric usage.
Improper hole size or spacing may cause clogging or insufficient drainage performance.
