This document is the Minimum and Maximum Cover Heights for Alternate HP Storm Pipe Technical Note. Various cover heights discussed.

Minimum cover for non-traffic rated applications (grass or landscape areas) is 300 mm (12”) from top of pipe to ground surface, for all pipe diameters. Additional cover may be required to prevent flotation.

The maximum burial depth is highly influenced by the type of backfill and level of compaction around the pipe. General maximum cover limits for HP Storm utilized in non-traffic rated storm drainage applications; using different backfill materials (split backfill) in the backfill zone.

Considerations that should be taken into account when a designer is determining the best backfill plan for a project:

1. Changing material types at the springline of the pipe requires accounting for the different soil confining strengths of the two materials. This variation in soil strengths can result in a reduced cover height when compared to an installation where a single material type is used for the entire pipe embedment. Where materials of differing strengths are used in the pipe embedment, susceptibility to pipe deflection can increase if the materials are not properly placed and compacted.

2. The fill heights are based upon a minimum compaction density of 85% being achieved for the native material above the pipe springline. When considering moisture contentand compaction effort, adequate compaction of Class 3 and 4 materials can be more difficult to achieve compared to the effort of a Class 1 material used in the haunch zone of the pipe.

3. When materials of different gradation are placed adjacent to each other, filter fabric separation or properly graded material, under the guidance of a geotechnical engineer, is recommended in order to prevent the migration of fines into the open-graded material.

An HP Storm Mechanical Properties table shows the resin, ASTM specifications, Allowable long term strain % and Initial/100 year psi. A figure showing the HP Storm Trench with uniform backfill, and a table with maximum cover for ADS HP Storm Pipe with split backfill measurements are included.