The new interchange is a median urban diamond design (see inset photo), with traffic now diverted over the railroad tracks.
“By shifting the road and putting the stormwater drainage underground, we were able to keep the existing landscape along the eastbound lanes of Grand Avenue. We were also able to separate the project into two work areas as opposed to three smaller areas. This helped with traffic and enabled the project to be accelerated. Having two large work areas meant we could do more work at a time.” The system was designed for a 100-year storm event with a capacity of 300 to 400 gallons per minute. More than 6,500 feet of Advanced Drainage Systems’ (ADS) N-12 corrugated HDPE pipe was used for the twin 54-inch-diameter runs. Additional N-12 pipe was used for the 18-, 24-, and 30-inch-diameter laterals. Depth of cover over the pipe ranged from 1 foot to 4 feet. The ADS pipe was also used to make modified manholes for access into the storm drain. The ADS plant in Phoenix manufactured the pipe and fabricated the fittings and man- holes, making just-in-time delivery possible. With a corrugated exterior and smooth interior, ADS N-12 HDPE pipe provided both strength and optimum hydraulic capacity. Because it is lightweight, ADS corrugated pipe was easily handled with minimal equipment by a one- or two-person crew, providing a favorable alterna- tive to concrete pipe. And with a long “stick” length of 20 feet, the number of joints were reduced, saving labor and installation time. Named for its Manning’s “n” rating of 0.012, the N-12 pipe was de- signed in 1987 by ADS specifically for culverts, storm sewers, high- ways, airports, and other civil design construction. ADS pipe is avail- able in diameters from 4 inches to 60 inches. Incorporating an integral bell and spigot, N-12 WT IB pipe meets ASTM watertight standards. The pipe’s structural capacity to withstand vehicle weight has been proven under Cooper E80 Loading conditions and has a rated use life of 100 years. The pipe’s strength is due to its design, HDPE resin, and manufactur- ing process, according to ADS. The structural integrity of corrugated HDPE pipe can be validated using the design procedures outlined in the AASHTO Load Resistance Factor Design (LRFD) Bridge Design
Specifications. AASHTO LRFD Section 12 is a strain-based design procedure suitable for thermoplastic pipes such as HDPE, polypropyl- ene, and PVC. The AASHTO LRFD code considers the actual failure modes of thermoplastic pipe such as thrust, wall buckling, as well as combined strain to ensure a viable design. Deflection is considered as a service limit and serves as confirmation of the design and ensures suitable long-term performance. Connections from the 54-inch pipe to the smaller laterals was done using the ADS Inserta Tee. The fittings are designed to provide a fast method of watertight lateral service connection for wastewater and stormwater pipe systems. Inserta Tees for 2- to 30-inch services readily fit ADS pipe. Inserta Tee fittings can also be used to connect corrugated metal pipe, PVC pipe, corrugated and solid-wall HDPE pipe, and pro- file wall pipe, regardless of the manufacturer. Inserta Tees meet ASTM 3212 air pressure testing and are watertight to meet project require- ments for storm and sanitary sewer lines. “One of the concerns that ADOT had was the maintenance and accessi- bility to the storm drain,” Brunker said. “So, we made manholes out of the ADS pipe that we could just drop into place and slurry backfill. We didn’t have to form up any manhole structures; we just used the pipe.” Using the HDPE pipe reduced the total budget by as much as 20 per- cent, which included materials and labor verses the alternatives of a ditch or concrete pipe. “The accessibility of the ADS product allowed the crew to come in, unload, and put it in,” Brunker stated. “It was a lot quicker process than it would have been with 54-inch concrete pipe. And speed was criti- cal because we were allowed to close down Bell Road for just seven months.”
Information provided by Advanced Drainage Systems (www.ads-pipe.com).
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february 2018
csengineermag.com
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