Quick and Efficient Installation

Polypropylene pipe helps Iowa utility add capacity to collections system in harsh winter conditions.
Quick and Efficient Installation
SaniTite HP pipe is rugged and lightweight, and is easily handled with minimal equipment and crew. Its stick length reduces the number of joints, which also saves time and labor. (Photos courtesy of Stephen C. Cooper)

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Heavy rainfall and increased demands overloaded the existing sanitary sewer system in Grimes, Iowa, and forced the municipality to add a new sanitary sewer line to its system. Rather than go the traditional route, engineers chose polypropylene pipe for the project, which reduced costs and sped up the installation.

“The project had to be done quickly and efficiently,” says John Gade, P.E., of FOX Engineering, and Grimes’ city engineer. “The actual work started in January and was completed in March 2012, not usually the ideal time of the year to be installing pipe in Iowa. Fortunately, we had two things going for us — the pipe itself and unusually mild weather.”

In late 2011, Grimes, located just west of Des Moines, experienced three consecutive days of heavy rain that overloaded the city’s existing sanitary system. The 24-inch outfall line carrying wastewater to the treatment plant backed up into the rest of the collections system, pushing graywater into residential basements. Grimes asked FOX Engineering to develop a plan to immediately address the overflow issue and add capacity to accommodate increased demands on the system attributed to a 67 percent growth in population between 2000 and 2010.

“Growth placed a lot of stress on the capacity of Grimes’ sanitary sewer system,” Gade says. “It is one of the most rapidly growing communities in the state and region. To provide for increasing industrial and residential development, the system was analyzed to determine which trunk mains needed to be replaced.

“We looked at the sanitary sewer that runs through a development corridor in Grimes and found that the 24-inch outfall line was near capacity and subject to added inflow and infiltration. Therefore, FOX Engineering recommended a new line be installed.”

The existing sewer line was made of clay and had been in the ground for nearly 40 years. The sanitary sewer improvement plan called for a new line to be installed parallel to the old one. Although the old line would be plugged, it could be temporarily unplugged in the future to accommodate maintenance on the new line.   

Picking the pipe

In selecting the pipe, FOX Engineering considered materials it had worked with in the past, including reinforced concrete, PVC, ductile iron and fiberglass. Engineers then met with Jim Merchlewitz and Paul Hutton of Advanced Drainage Systems Inc. (ADS) to review the company’s SaniTite HP polypropylene pipe and learn more about projects in which the product had been used.

Based on an analysis of the product, FOX Engineering determined it was durable enough to meet all the needs for the new outfall line. While not part of the original analysis, it also turned out that the ADS pipe had a price advantage over other products evaluated.

A total of 1,857 feet of 48-inch-diameter and 3,000 feet of 36-inch-diameter SaniTite HP pipe was used for the project, along with A-LOK connections to the concrete manholes.

Manufactured in 30- to 60-inch diameters, SaniTite HP pipe is available in triple-wall construction that provides a smooth interior and exterior wall design supported by a corrugated structural core for improved stiffness and greater beam strength to minimize deflection and enhance long-term performance. It meets ASTM F2736, ASTM F2764 and also exceeds the requirements of ASTM D3212 for water tightness with dual-gaskets and banded reinforced bells.

The lightweight pipe is easily handled with minimal equipment and crew. Its stick length reduces the number of joints, which also saves time and labor and makes for a more secure system versus the shorter, heavier sections of some other pipe.

Convenience and flexibility

The sanitary sewer line was installed by Keller Construction Inc. of Boone, Iowa. “I like the product,” says owner Darin Keller. “It’s the first time we used triple-wall SaniTite HP, but we have used a lot of the black ADS corrugated HDPE pipe for stormwater projects, most recently 5,000 feet.

“Merchlewitz and Hutton also told me about using the A-LOK mount. For the triple wall, SaniTite HP pipe, which is smoother than the corrugated HDPE pipe, fits really tight and there’s no need to grout,” Keller continues. “The pipe does not need any additional adapters to fit into the precast manhole with A-LOK Premium gaskets, making our installation fast, and still giving us flexibility in the field. We had no leaks, no problems. The A-LOK units work well with the precast concrete manholes and the polypropylene pipe.”

Keller says the convenient pipe length also made installation easier. “We used a 13-foot-long pipe instead of a 20-foot pipe because the trench box is 25 feet long. The shorter pipe gave us room on each side for safety. When we’re 20 feet deep, it’s too much of a reach for our excavator. We used a John Deere 450, 110,000-class machine.”

Backfill consisted of a bed of rock over the top of the pipe, followed by the native soil.

“The ADS pipe made the job easier. The pipe isn’t heavy, and you can drop it from 20 feet in the air and it’s not going to break, even in the winter,” Keller says. He also noted there was no worry about installing the pipe in cold weather, or chipping or cracking the pipe or any components.

During the installation in Grimes, on-site visits were conducted by representatives from the Iowa DOT and Iowa’s Statewide Urban Design and Specifications (SUDAS), the organization responsible for developing common design standards and specifications for public improvements such as sanitary sewers.

“After the job was finished we vacuum and pressure tested,” Keller says. He also put his 10 years of knowledge into a true hands-on effort. “I actually went inside and mandrelled the pipe. I crawled through the run to see if there were any issues with the pipe. Overall, the pipe went in good and tested good. We saw very little deflection. We also tested the joints, all of which were fine.”


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