Review of Design Methods in AWWA Manuals for Various Flexible Pipe

For pressure pipe applications, the American Water Works Association (AWWA) publishes manuals that provide design and installation guidelines for PVC, HDPE, fiberglass, steel, ductile iron, and concrete pipe. Unfortunately, there is little uniformity in these manuals for flexible pipe design and installation and that creates uncertainty, confusion, and wasted time. Consistency and simplicity will promote practices that will result in better pipeline projects and save money. While based on the early theoretical and empirical basis as presented by Merlin Spangler, and later modified by his student Reynold Watkins in the modified Iowa equation, the method of calculating deflection of flexible pipe has evolved somewhat independently for the different pipe types. As a result, representatives for each type of pipe material developed different guidelines specific to that pipe which then made their way into the various AWWA manuals. Consequently, this has resulted in nonuniformities that include varying schools of thought on the factors that affect E’, differences in E’ values, use of the deflection lag factor, D_L, differences in basic terminology, use of the constrained soil modulus, M_s, acceptance or rejection of composite E’, and use of multiple classification systems for the same soil types. Pertaining to installation, the differences include trench section terminology, trench widths, and bedding thicknesses. This paper will provide an in-depth review and comparison of buried flexible pipe design and installation as addressed in each of the AWWA manuals of water supply practice for the six previously mentioned pipe materials: M23 (PVC), M55 (HDPE), M45 (GFRP), M41 (DIP), M11 (steel), and M9 (Bar-wrapped CCP). Revisions to create uniformity and consistency in the manuals are suggested. A single manual dedicated to external load design and installation may be a solution. It could then be referenced in the current manuals.