This technical document provides maximum cover height values for split backfill condition installations using HDPE Storm Pipe, Alt. Embedment – CSA Pipe only for storm drain applications.

Fill heights presented in this technical note are applicable to 100mm through 900mm diameter ADS N-12®, N-12® ST, and N-12® WT pipe certified to CSA B182.8 “Profile Polyethylene (PE) Storm Sewer and Drainage Pipe and Fittings.”

Figure one shows the ADS N-12 (CSA B182.8) HDPE Storm Pipe Split Backfill Trench Detail as a diagram. Table 1 shows the ADS N-12 (CSA B182.8) HDPE Mechanical Properties. Table 2 shows the Maximum Cover for ADS N-12 (CSA B182.8) HDPE Storm Pipe in Split Backfill, m (ft). Maximum cover limits for ADS N-12 (CSA B182.8) HDPE pipe used in storm drainage applications are shown in Table 2 for split backfill conditions.

The maximum burial depth is highly influenced by the type of backfill and level of compaction around the pipe. Changing backfill 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. 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.

Backfilling and compaction specifications indicate that select native clean backfill shall be well-placed, well-compacted (95% SPD) Class IV or Class III per ASTM D2321 with no foreign debris including rocks, large clumps of organic or frozen material.