What is the minimum cover for the pipe?

The minimum cover for HDPE pipe is 1'-0" for H-20 traffic loads if installed in accordance with AASHTO Section 30. This is based on empirical calculation of load response, manufacturer's testing and field experience with the pipe. AASHTO specifications Section 18.4.1.5 defines the minimum cover as "ID/8 but not less than 12 inches." This cover is measured from the pipe OD to the top of a rigid (concrete) pavement or the bottom of a flexible (bituminous) pavement. Both AASHTO and ASTM, as well as most manufacturers, require additional (temporary) cover for construction loads greater than H-20. Generally, an additional 2' of temporary cover, mounded over the pipe and removed for final grading and paving, is sufficient for large construction vehicle loads.