Effective Point Repair Of Laterals

Laterals – 4th In A Series
January 2011 Vol. 66 No. 1

Acrylamide chemical grout is the thinnest product on the market. It has the same viscosity as water and becomes a firm, impermeable gel within a controllable time frame (anywhere from 5 seconds to 10 hours). Because it is a true solution-grout (no suspended solids) and has such low viscosity, it easily penetrates annular spaces and soil outside of pipes. Once the grout cures it will seal the pipe from infiltration/exfiltration, stabilize the soil around the pipe and lock the pipe in place at the points of injection. Acrylamide chemical grout’s longevity in the soil, low viscosity, controllable cure time and 60-plus year history make it the most widely used grout for controlling groundwater.

Acrylic gel (NMA) is a water solution of acrylic resins used similarly to acrylamide chemical grout. Because the behavior of the materials can be closely controlled under leak flow conditions, acrylic gels are also used for sealing leaks in mainlines, manholes or other below grade structures.

Acrylate grouts have been introduced into the sewer sealing and geotechnical industry over the past 25 years. Acrylate grouts have not gained widespread acceptance because they create weak gels and swell considerably in the presence of water.

Urethane grouts have a long history of success in stopping infiltration in underground structures. However, they are stickier than other grouts and require more effort to keep pumping equipment clean. They are also moisture activated which means special steps must be taken to keep moisture out of the hoses and pumping equipment. Urethane gels are pumped at a 7:1 or 8:1 ratio of water to resin so the pump equipment must be set up to pump multiple ratios; in contrast to the acrylics which are pumped at a 1:1 ratio of Part A to Part B. When comparing ease of use, cost of product, viscosity and controllability of the cure-time, urethanes are used far less in lateral rehabilitation than acrylamide/acrylic gels.

Grout application
Grout typically is applied to reinstated mainline-lateral connections, and Anctil said a detailed closed-circuit television inspection of the laterals can also find other defects higher in the lateral that allow infiltration during high groundwater tables.

Grout is applied by positioning and inflating the grout packer over a defect.