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When ‘Old School’ is the Right School: Combined Grout, CIPP Effective Solution For Illinois City
It wasn’t just pipe diameters that were big on this project; the sheer scale was also a challenge. To support fieldwork, Walden’s staff designed and customized a 48-foot, temperature-controlled semi-trailer. “We set it up so that we could mix two, 120-gallon batches of grout at a time and keep them warm in the trailer until they were transferred to the grout truck just before pumping,” Bohn explains, “We also used the trailer to store all chemicals and safety equipment. We even had the inspector’s desk in there, with video monitors and hardwired audio communications right at the desk -- our crews were never out of touch with surface support.”
With the custom trailer and the right equipment in place, Walden was able to stick to a very productive schedule. Working in two, 12-hour shifts per day, five days per week, Walden crews were able to test, grout and re-test 20 joints per shift on most of the sewers, and 12 to 14 joints per shift when working on 108-inch pipe.
“Most of that time was devoted to moving the packer between joints and doing the pre- and post- air testing,” says Bohn, “Actual grout application goes quickly.”
One accommodation made for the larger diameter pipe was to extend curing times. Whereas small diameter joints can set up in as little as 30 seconds, 90 seconds were allotted for full cure times on the large diameter pipes. “On larger pipes, it’s important to slow down a bit,” says Bohn, “That way, it sets up well, and you get a good grout band around the outside of the joint.”
Pumping out the work
Work began on Jan. 10, 2012, and continued through summer. “Sewer work is a little easier in winter and summer, when the river—and, consequently, the groundwater—is relatively low,” Osborn says, “But chemical grouting could be done in spring as well, and we had no problems sticking to our schedule.”
The solution grout used was AV-100 acrylamide grout from Avanti International. The exact mix was 50 pounds of AV-100 dissolved in 30 gallons of water providing a 20 percent solids mix. This becomes a 10 percent solids mix when an equal volume of ammonium persulfate solution (used as a catalyst) is added. This grout mix was supplemented with two gallons of Avanti AV-257 Icoset per 60-gallon batch -- the AV257 is a latex-based product that increases the flexibility of acrylamide grout, and was added for additional protection against groundwater-induced movement in the Granite City sewers.