Reinforced concrete pipe was the foundation for the major Pennsylvania road project.
Engineers had to consider loosened shale and bedrock, bogs hidden under the ground, and the possibility of landslides.
They manufacture 12- through 120-inch rubber gasket and mortar joint pipe, 18- through 108-inch elliptical pipe/flared ends, and 12-inch through 72-inch round/elliptical.
“Using the 72-inch pipe in place of box culverts in some areas was a major cost savings for PennDOT,” says Loomis-Major. “Normal Class V pipe at 3000D would not have been adequate to withstand the loads, so a special design pipe was utilized.”
There were two runs of 72-inch heavy wall RCP. The first was 528 linear feet with a fill height of 60 feet; the other with 320 linear feet at a height of 40 feet fill. The solution was to design and manufacture a 72-inch heavy-wall RCP that could withstand a D-load of 4841 linear feet per pound for the 60-foot fill and 3232 linear feet per pound for the 40-foot fill. This phase included additional runs of 30-inch and 36-inch heavy wall pipe with 30 feet of fill.Planning for delivery
Transporting 1250 tons, or 200 truckloads, of concrete pipe required careful planning by the plants' production and dispatching departments. The 72-inch, 60-foot fill pipe weighed 35,000 pounds per section. That limited payload to one 8-foot pipe per truck. The haul from the Montrose plant to the site was a relatively short run of 130 miles a round trip. But the trip from the Farmingdale plant covered almost 450 miles.
The 72-inch type required a steel area of 1.251 sq.in/ft inner and 0.444 sq. in/ft outer with a concrete mix design of 6000 psi. The 7¾-inch wall thickness product had 1¼-inch cover over the reinforcement.
The 72-inch type had a wall thickness of 14-inch with 1-inch cover over the reinforcement. Using special forms and equipment, including additional vibration, Kerr was able to produce four 8-foot sections per day with a dry cast process. Each section weighed 17 tons.
The steel area consisted of a 0.616-square-inch/foot inner and a 0.190 square inch/foot outer with a concrete strength of 6000 psi. Four-inch diameter lift holes were installed in both sets of pipe to facilitate the “teacup” lifting mechanism.
PAIDD performance specifications include a 1.43 factor of safety for field cracking with a 0.7 crack control factor. As a result, crack width is limited to .007 for acceptance during 3EB testing. These specially designed and manufactured pipe passed this test while less than 28 days old.
“Because of the project's complexities, it was beneficial for us to work with one supplier,” says Ridall. “We have obtained a consistency throughout the job and a solid working relationship. Schedules were more easily met, and any obstacles that arose were handled quickly.” Work should be completed and the new highway opened to traffic by fall 2008.
— Mary Beth Kramer is a freelance writer in Pennsylvania.