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Rehabilitating A New Sewer: Village of Bradley Eliminates I&I With Chemical Grouting
One repair option that the city experimented with was oakum packing and cement patches. That combination works on small leaks, but the cracks and failures in the manholes were just too large and water pressures too high.
Chemical grouting seemed a perfect solution for the situation. A trenchless method that has proven itself over 50 years, grouting works by filling the soil voids behind leaks and cracks with an acrylamide solution that quickly sets up into a durable rubbery gel, creating a gasket-like seal that plugs leaks and stabilizes the surrounding bedding, thus ending the process that caused the problem in the first place. Fixes can last decades and are far less expensive than other trenchless methods. If long sections of pipe don’t need replacing or relining, grouting is often the best repair technique available.
But there is one catch: grouting requires skillful application to work well – it is not as straightforward a process as replacement or relining. The village contacted Visu-Sewer, a Wisconsin-based company that they had worked with previously. “They were the only ones we knew who did this work,” Williams explains, “They’d done good work in the village on other projects. We knew they were experienced and that they were a good choice for this project.”
A tricky job done right
Injection grouting can seem like a fairly simple process. Holes are drilled near leaks and a solution of acrylamide and catalyst is injected into the bedding outside the leak. The solution is mixed right at the applicator tip as the chemicals are injected. If all goes well, the solution flows to the infiltration areas and sets up there, plugging the leak and filling the external voids caused by soil washing into the pipe.
“But every manhole is different,” says Visu-Sewer Foreman Keith Mauzer. “In this case, some inverts were cracked, and there were also cracks around the ‘bench’ where the precast manholes were set into the trench. You have to develop a sense of where to drill ‘away’ from leaks, and gauge the curing time correctly so that the solution flows to the leak and sets up as it gets there. It’s a bit of an art.”
The two-man Visu-Sewer crew worked on one manhole per day and dewatered with an upstream inflatable plug as they went. But the plug didn’t make things dry. “There was a lot of groundwater in the surrounding bedding and it got higher and higher as the job progressed” Mauzer explains. “Even on the first manhole, water was coming into the pipe through leaks at about five to 10 gallons per minute at each manhole -- and it got worse as we went along.”