Polymer Concrete Manholes Defeat Corrosion in Sewer Rehab Project

by Jeffrey LeBlanc

A recent project featured the installation of polymer concrete manholes to prevent corrosion and erosion in a rehabilitated Lansing, MI, sewer line. Amitech USA fabricated a customized junction chamber and 20 replacement manholes of Meyer Polycrete Polymer for the city’s Westside Interceptor Phase IV-C Project.

The existing manholes had been eroded by turbulence in the sanitary sewer line and had been damaged by hydrogen sulfide corrosion. The pipes of the Westside Interceptor had been relined with various materials about three years ago but the manholes had not been replaced or upgraded.

The segment of the West Side Interceptor receiving the new manholes was about 7,000 feet long. Several of the manholes were on the property of an inactive General Motors Corp. auto assembly plant.

The replacement manholes each consisted of a flat-paneled lower unit reducing to a standard 48 inch riser and cone section.

Lansing’s sanitary sewer service area covers 27,000 acres and includes the city, Lansing Township, and parts of four other townships. The sewer system has 850 miles of lines and 15,000 manholes.

The city’s public works department and contractor Tetra Tech selected Amitech’s Meyer Polycrete product as their replacement material for the manholes. Dunnigan Brothers Construction Co. removed the old manholes and installed the new ones from July to December of last year.

The units are expected to last a minimum of 50 years and could last twice as long. The polymer concrete, developed in Germany, has only been available in the U.S. since Amitech built a plant at Zachary, LA, in 2004.

Using polymer concrete provided the long-term chemical resistance that the city wanted and also facilitated faster installation. The 20 prefabricated manholes had outer dimensions of 6 by 9 feet, fitting within the footprint of the old manholes, which were 10 feet in diameter.

Preparing the junction box for pipe installation

The smaller configuration also helped minimize disruption. The city wanted to avoid damage to the existing, relined pipe system, as well as reduce disruption on the surface, where much of the work was in or adjacent to public streets.

The replacement manholes each consisted of a flat-paneled lower unit reducing to a standard 48 inch riser and cone section. That design was chosen to accommodate the connections between manholes and the various pipe shapes and orientations. The four- or five-sided paneled lower units required the smallest construction area possible while accommodating the large diameter sewer pipe connections.

The existing nonstandard pipe sizes ranged from 51 to 58 inches and included some sections of 46 by 72 inch elliptical concrete pipe. During the replacement process, the existing pipes were cut back far enough to allow for the installation of the manholes. That required short sections of new pipe to join the manholes to existing pipes. Amitech made custom-dimensioned Polycrete Polymer pipes molded to match the inside and outside diameters of the existing concrete pipe. The pipe connections to the new structures were made with flexible boots and the connections to the existing pipes were sealed with concrete collars.

The junction chamber was a challenge because Amitech had to prefabricate a structure to match the existing horizontal and vertical alignments of the three incoming pipes that were to be connected. The chamber joined flows from a 48 inch gravity line and a 24 inch force main, converging them into a 54 inch gravity line.

Amitech made the junction chamber in three pieces: a cover slab with three hatch openings, a riser section, and the lower chamber. The latter had factory installed channels, stop logs, sluice gates and polymer coated benching.

The use of a preassembled chamber facilitated the installation. Epoxy mortar was used to join the lower unit to the upper section and cover slab. At 26 tons, the lower unit was the heaviest piece ever cast at Amitech’s Zachary plant. A 200-ton truck crane was used to place the chamber components at Lansing.

Patrick Dunnigan, of Jackson, Michigan-based Dunnigan Brothers Construction, was project manager for the Westside Interceptor upgrade.

“The Amitech manholes went in good and were well made. We didn’t have any difficulty with them even though a few of them were placed relatively deep in the ground. After we did the first few manholes, we were installing one a week,” Dunnigan said.

Meyer Polycrete Polymer is designed for use in a variety of sanitary, storm and industrial sewer applications. The product is especially well suited for highly corrosive environments, since it eliminates the need for linings, coatings and cathodic protection. The polymer pipe’s strength and rigidity has made it a choice for microtunneling and pipe jacking applications. It currently can be cast in diameters of 12” to 102” and joint lengths of up to 10 feet.

About the Author:

Jeffery LeBlanc is a professional engineer with expertise in civil engineering. A Louisiana State University graduate, he has been with Amitech USA for three years. He is a member of ASTM International and American Water Works Association committees that are charged with developing standards for polymer concrete and fiberglass pipes.