What follows is an article I initially penned for the February 2002 Parameter, the newsletter of the Central Virginia Chapter of the Construction Specifications Institute (CSI). the original title was Division Two: Plastic Storm Piping. It should be noted that since the adoption of MasterFormat 2004™ and the subsequent withdrawal of support for MasterFormat 95™, Division Two (Division 02) (formerly Sitework) has been reassigned to Existing Conditions. Sitework has been moved to various divisions in the 30’s.
DIVISION THIRTY-THREE: PLASTIC STORMWATER PIPING
— Raymond E. Gaines, AIA, FCSI, CCS
For generations, storm drainage piping has remained essentially unchanged. Designers specified and the industry used reinforced concrete pipe (RCP) or corrugated metal pipe (CMP) for larger sizes and terra cotta, cast iron, and similar materials for smaller applications. Other structures (manholes, drop inlets, etc.) were made of masonry of some kind, either brick and block, cast in place concrete, or precast. Precast has been the dominant material used for these in recent years, but the other materials remain in use, to a lesser degree depending on the preferences of the contractor/installer.
In the last several years, plastic materials have entered the marketplace. In the (1970’s) plastic pipe came into use for applications of 8” (20cm) or less, and was frequently used for roof drainage. These included Polyvinyl Chloride (PVC), ABS, and others. Their use as catchment piping for larger paved areas was limited, of course, by their size.
Over the last twenty years or so, the industry has gone to High Density Polyethylene (HDPE) for large diameter piping with increasing frequency. It is usually used in corrugated form with smooth interior walls. Interior friction is slightly less than for RCP, so flow characteristics are similar to slightly better. The HDPE pipe can be used with conventional masonry drainage structures (manholes, etc.) or with plastic structures that the manufacturers are promoting now. These materials are rated for AASHTO loads when installed properly Plastic piping and related materials should comply with applicable ASTM and AASHTO standards.
When installing plastic storm piping materials, meticulous care needs to be exercised to follow the manufacturer’s instructions and recommendations. This is of particular importance in backfilling and protection from direct sunlight.
When properly backfilled, the piping is resistant to crushing due to arching action of the backfill. Conversely, voids in the backfill could allow deformation of the pipe under load. Because of this, an appropriate inspection and testing program is strongly recommended. Backfill should be placed and compacted in accordance with applicable AASHTO and ASTM standards.
Certain plastics degrade when exposed to Ultra-Violet (UV) light/radiation. The piping manufacturers have recommended certain end details to prevent said degradation. If using plastic piping in applications where exposure to sunlight is a possibility, the designer and installer need to verify that the specific piping material is intended for such exposure.
Other important considerations include volume of flow and buoyancy. The last two are particularly important given the light weight of plastic materials compared to RCP.
When properly installed and maintained, the newer materials produce a satisfactory project with a long life.
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