TN 1.01 Dual Wall HDPE Perforation Patterns is a technical note that describes the classifications and pattern types available for perforated pipe.

Perforated pipe plays an integral role in many applications of HDPE pipe. Perforated pipe is used to accelerate the removal of subsurface water in soils or to allow storm water to percolate into the soil.

Currently, two classifications of perforations are specified in the AASHTO material specifications for HDPE pipe: Class I and Class II. The Class II perforation pattern comes standard when perforated pipe is ordered. Class I perforated pipe has limited availability. Both classes are explained in more detail in the AASHTO materials specifications (M294 and M252). AASHTO M252 covers pipe diameters 3-through 10-inch (75 - 250 mm) while M294 covers 12-inch through 60-inch (300 - 1500 mm).

Terminology for perforations is derived from the applicable AASHTO specification. Class II perforations shall be located in the outside valleys of the corrugations, be circular and/or slotted and evenly spaced around the circumference and length of the pipe.

The perforations shall be located in the outside valleys of the corrugations. The water inlet area shall be no less than 0.945 in 2/ft (20 cm2/m) for pipe diameters 4- through 10-inch (100 - 250mm), 1.42 in 2/ft (30 cm2/m) for pipe diameters 12”-18” (300 - 450 mm) and 1.89 in2 /ft (40 cm2 /m) for pipe diameters larger than and equal to 24” (600 mm). Table 1, included in this document, represents ADS standard perforation patterns for AASHTO Class II.

This technical note includes several diagrams for AASHTO Class II Perforation Patterns, including different pipe diameters, rotations, numbers of holes around the circumference based on diameter and region.

Class I perforation patterns are approximately circular and arranged in rows parallel to the axis of the pipe. The locations of the perforations shall be in the valley of the outside of every corrugation. The perforations shall be arranged in two equal groups placed symmetrically on either side of the lower half of the pipe. Diameters 4”-10” are not available in Class I patterns, however your local ADS representative may be contacted to verify whether your custom pattern can be provided.