Structural Design of Flexible Conduits

The Natural Resources Conservation Service (NRCS) has used flexible pipe in embankment dams throughout its history. Corrugated Metal Pipe (CMP), Corrugated Plastic Pipe, and solid wall plastic pipe are often used on NRCS dams. Flexible pipe is only allowed as a principal spillway conduit on Class A (Low Hazard Dams) as described in NRCS Conservation Practice Standard 378 and Technical Release 60 - Earth Dams and Reservoirs with a storage times effective height product of less than 10,000. In addition to flexible pipes being used as principal spillway conduits, flexible pipe is often included in foundation drain systems or as outlets for chimney drains or seepage diaphragms in larger structures. The structural design of the flexible pipe has historically been based on the deflection criteria in NRCS Technical Release 77 - Design and Installation of Flexible Conduits. The NRCS is currently updating the agency's design guidance to be more comparable with industry standard design practice. This paper will present a comparison between the historical NRCS design procedure versus current industry practice. The paper will also illustrate the differences in the design for a CMP principal spillway conduit and a plastic drain pipe. 15 pp., 5 tables, 4 figures, 9 references.