AWWA Design Window
AWWA M-55, PE Pipe Design and Installation describes a Design Window, for which minimal calculations are necessary to verify if the pipe can withstand the anticipated external loads. Furthermore, no calculations are required for HDPE operating within the Design Window and having a DR21 (or less). The Design Window specifications are:
- Pipe made from stress-rated PE material.
- Essentially no surcharge (surface) load imposed over the pipe, no ground water above the surface, and provisions for preventing flotation of shallow cover pipe have been provided.
- The embedment materials are coarse-grained, compacted to ≥ 85% Standard Proctor Density and have an E' (modulus of soil reaction) value ≥ 1000 psi. The native soil must be stable; i.e., the native soil must have an E' ≥ 1000 psi.
- The unit weight of the native soil ≤ 120 pcf.
- The pipe is installed in accordance with manufacturer's recommendations for controlling shear and bending loads and minimum bending radius, and installed in accordance with ASTM International D2774, Standard Practice for Underground Installation of Thermoplastic Pressure Piping for pressure pipes, or ASTM International D2321, Standard Practice for Underground Installation of Thermoplastic Pipe for Sewers and Other Gravity-Flow Applications for non-pressure pipes.
- Minimum depth of cover is 2 ft; except when subject to AASHTO H20 truck loadings, in which case the minimum depth of cover is 3 ft or one pipe diameter.
- Maximum depth of cover is 25 ft.