The Importance of the Gradation of Sands With Respect to Structural Backfill Support for Plastic Pipe
The engineering community must design their projects with consideration given to gradient control of the backfill envelope. As the AASHTO Section 12 Plastic Pipe Design procedure warns, uniformly graded material with an average particle size smaller than a No. 40 sieve “should not be used as backfill for thermoplastic culverts.” If, however, the design engineer allows the use of such material, that decision requires extra precautions during design and installation.
