Storm drain installations have a minimum and maximum burial depth for corrugated HDPE Pipe per CSA B182.8. This technical note provides information on fill heights for open profile 100 mm (4”) through 1500 mm (60”) ADS N-12®, N-12 ST, and N-12 WT pipe manufactured in accordance with CSA B182.8.

The two common cover height concerns are minimum cover in areas exposed to vehicular traffic and maximum cover heights. Either may be considered "worst case" scenarios from a loading perspective, depending on the project conditions.

The minimum cover required when the drainage system is in a traffic area with drainage pipe diameters from 100 mm through 1200 mm (4”-48”) must have at least 0.3 m (12”) of cover over the pipe crown, while 1500 mm (60”) pipes must have at least 0.6 m (24”) of cover. If settlement or rutting is a concern, it may be appropriate to extend the structural backfill to grade. Where pavement is involved, sub-base material can be considered in the minimum burial depth. While rigid pavements can be included in the minimum cover, the thickness of flexible pavements should not be included in the minimum cover.

The maximum burial depth is highly influenced by the type of backfill and level of compaction around the drainage pipe. General maximum cover limits for 100 mm (4”) through 1500 mm (60”) ADS N-12, N-12 ST, N-12 WT ADS HDPE dual wall pipe per CSA B182.8 are shown in Table 3 for a variety of backfill conditions.

Table 1 and Table 3 show installation of ADS HDPE pipe under pavement using a uniform backfill type and compaction level. All calculations assume zero hydrostatic load around the pipe, incorporate the maximum safety factors represented in structures section of the Drainage Handbook, use material properties consistent with the expected performance characteristics for ADS HDPE dual wall pipe materials per CSA B182.8.

Refer to the Drainage Handbook for additional information that may affect the cover requirements in the Installation section (Section 5).