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378-5 Fond <br />• All pipe uoints shall be made <br />watertight by the use of <br />couplings, gaskets, caulking, or <br />by welding. <br />For dams 20 ft. or less in <br />effective height, acceptable pipe <br />materials are cast-iron, steel, <br />corrugated steel, or aluminum, <br />asbestos-cement, concrete, <br />plastic, vitrified clay with <br />rubber gaskets,.and.cast^in-place <br />reinforced concrete. Asbestos- <br />cement, concrete, and vitrified <br />clay pipe shall be laid in a <br />concrete bedding. Plastic pipe <br />that will be exposed to direct <br />sunlight shall be made of <br />ultraviolet-resistant materials <br />and protected by coating or <br />shielding, or provisions for <br />replacement should be made as <br />necessary. Connections of plastic <br />• pipe to less flexible pipe or <br />structures must be designed to <br />avoid stress concentrations that <br />could rupture the plastic. <br />For dams more than 20 ft. in <br />effective height, conduits shall <br />be plastic, reinforced concrete, <br />cast-in-place reinforced concrete, <br />corrugated steel or aluminum, or <br />welded steel pipe. The maximum <br />height of fill over any principal <br />spillway steel or aluminum pipe <br />must not exceed 25 r"t. Pipe sha41 <br />be watertight. The joints between <br />sections of pipe shall be desioned <br />to remain watertight after joint <br />elongation caused by foundation <br />consolidation. Concrete pipe <br />shall have concrete bedding or a <br />concrete cradle, if required. <br />Cantilever outlet sections, if <br />used, shall be desioned to <br />withstand the cantilever load. <br />Pipe supports shall be provided <br />when needed. Other suitable <br />• devices such as a Saint Anthony <br />Falls stilling basin or an impact <br />basin may be used to provide a <br />safe outlet. Protective coatings <br />of.asbestos-bonded, asphalt <br />coated, polymeric or vinyl coating <br />on galvanized corrugated metal <br />pipe, or coal tar enamel on welded <br />steel pipe should be provided in <br />areas that have a history of pipe <br />corrosion, or where the saturated <br />soil resistivity is less than <br />4,000 ohms-cm, or where soil pH is <br />lower than 5. <br />Specifications in tables 2 and 3 <br />are to be followed for polyvinyl <br />chloride (PVC>, steel, and <br />aluminum pipe. <br />Cathodic protection is to be <br />provided for coated welded steel <br />and galvanized corrugated metal <br />pipe where soil and resistivity <br />studies indicate that the pipe <br />needs a protective coating, and <br />where the need and importance of <br />the structure warrant additional <br />protection and longevity. If <br />cathodic protection is not <br />provided for in the original <br />design and installation, <br />electrical continuity in the form <br />of joint-bridging straps should be <br />considered on pipes that have <br />protective coatings. Cathodic <br />SCS, Colorado. January ]qR4 <br />