This document is the TN 2.04A Minimum Maximum Cover Heights for Alternate Trench for HP Storm Pipe Trench. Minimum and maximum covers are supported by tables.

The information in this document is designed to provide answers regarding general cover heights questions regarding the alternative trench installation of ADS HP Storm pipe; the data provided is based on Culvert Analysis and Design (CANDE) with information presented in the Structures section (Section 2) of the Drainage Handbook. Project specific properties should be included in analysis for specific project design.

Minimum cover for non-traffic rated applications (grass or landscape areas) is 12” (300mm) 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 ADS HP Storm utilized in non-traffic rated storm drainage applications; using different backfill materials (split backfill) in the backfill zone.

Table 1 shows the values for the ADS HP Storm Mechanical Properties. Figure 1 shows the ADS HP Storm Pipe Split Backfill Trench Design. Table 2 shows the maximum cover for ADS HP Storm Pipe with Split Backfill.

Notes state that results based CANDE analysis. Calculations assume no hydrostatic pressure and a soil density of 120 pcf (1926kg/m3) for overburden material. Backfill materials and compaction levels not shown in the table may also be acceptable. Class 1 material used below springline must be adequately “knifed” into haunch and in between corrugations. Unless otherwise noted by the engineer class I material must be compacted in 6-inch (200mm) lifts. Select native clean backfill shall be well placed, moderately compacted (85% SPD) Class IV or better per ASTM D2321 with no foreign debris including rocks, large clumps of organic or frozen material. For projects where cover exceeds the maximum values listed above, contact ADS for specific design considerations.