Trenchless keeps traffic moving.

Because infrastructure repairs are an ongoing concern of municipalities, finding cost-effective solutions to both emergency repairs and regular maintenance is a daily challenge faced by public works departments. While a Chicago public works team was inspecting targeted sections of older pipe as part of its preventive maintenance program, it discovered a collapsed section of brick sewer, which resulted in roadway damage and expensive emergency repair work.

After the situation was under control, the city initiated a survey of the entire pipeline to troubleshoot future problems. The survey revealed that much of the pipe was in need of some kind of repair, including another 170-foot section near collapse. The city’s immediate goal was to repair this pipe without completely shutting down traffic flow. The best option was trenchless pipeline reconstruction, using a corrosion-resistant, structurally sound cured-in-place pipe (CIPP).

Public works officials worked with InLiner USA/Kenny Construction, Chicago, to complete the repairs. Because the pipe was located underneath a major thoroughfare with elevated railroad tracks passing over the road, the workers were concerned that the vibrations could cause the structure to collapse at any time. “During the inspection you could see the asphalt in the road from the voids at the crown of the pipe,” says Ralph Bonanotte, project supervisor.

Normally, the pipe would have been cleaned prior to installation of the CIPP, but due to the possibility of collapse, this was not possible. “We had to avoid the normal cleaning techniques for fear that the sewer would collapse even more,” Bonanotte says. Grout was used to fill the large voids after the combined sewer was relined as a safety precaution to stabilize the area surrounding the pipe. In addition, possible damage to the overhead railroad supports was avoided.

The inversion process involves a pliable felt tubular liner saturated with a thermosetting vinyl resin, which is pulled through from manhole to manhole. An internal calibration hose is inverted into the existing tube and forced through the liner with a column of water. This hydrostatic water pressure causes the tube to fuse with any irregular shapes of the existing pipe. Hot water circulated though the pipe hardens the tube, forming a self-supporting “pipe-within-a-pipe” that is structurally sound, jointless and impermeable with a unique locking bond to the host pipe.

The resin flows into cracks and voids during the inversion process, reducing infiltration and exfiltration. Finally, the ends of the pipe are trimmed and service lateral connections are reinstated using camera-equipped, remote-controlled robotic cutters.

The flexible CIPP process can reconstruct hundreds of feet of pipe ranging from 3 inches to 96 inches in diameter, accommodating any offsets and bends. Cured-in-place pipe also resists long-term corrosion and stops root intrusion.