The 4Ps of Sealing Laterals with Chemical Grout
The Problem, Procedure, Product and Promise
Dec 02, 2013
Finding answers to rehabilitate and sustain our declining underground infrastructure is easy. There are many. Finding the optimum answer is another story.
Pipe lining is a common rehabilitation method that is used to renew structurally damaged pipes and reduce infiltration. However, reinstating laterals provides an avenue for all the groundwater moving freely through the annular space between the liner and the host pipe to enter the collection system. Further, even pipes that are in sound structural condition can have infiltration through defective joints and lateral connections. By reviewing the problem, procedure, product and promise, here’s a quick look at the most cost-effective answer to sealing laterals and lateral connections with chemical grout.
ProblemThe EPA estimates there are more than 70 million laterals in the United States and a large percentage of these laterals are leaking or in need of some kind of repair. These leaking laterals account for more than 50 percent of the infiltration in our collection systems. Infiltration introduces groundwater and fines from the surrounding soil into the collection system, which erodes the pipe bedding and leads to deterioration of the pipe. This excess water and sand have to be treated and dealt with by the treatment facility downstream at a high cost to the public.
Defective joints and lateral connections, as well as the annular space outside of a pipe liner, can be grouted to completely seal off the path of least resistance for the water infiltration. By using remote grouting equipment, leaking laterals can be chemically grouted using an acrylic or urethane gel material. An operator inserts a camera and remote lateral grout packer through a manhole opening (typical access) and positions a winch system in another manhole to complete the equipment set up. The camera is used to locate the leaking lateral and positions the lateral packer at the cut-out where the lateral was reinstated. The operator inverts a bladder up the lateral then inflates the bladders on the packer, then inverts a bladder up the lateral to seal off the mainline and the first few joints up the lateral and begins pressure injecting the grout material into the leaking area to completely fill the annulus and any voids surrounding the pipes.
The chemically-activated grouts initially have the same viscosity as water to maximize permeability into the voids surrounding the defects. In 30 to 60 seconds after pumping the grout, it creates a gel-soil matrix on the outside of the pipe to produce an effective, long-lasting water barrier while providing superb soil stabilization and pipe support. A rule of thumb is followed by the operator when grouting laterals: typically, he/she will pump a quarter- to half-gallon of chemical grout per inch diameter of mainline pipe sealing the lateral connection, plus 1 gallon per ft of lateral to be sealed. For example, to grout 3 ft up a 4-in. wide lateral connection to an 8-in. mainline, the contractor would try to pump (2+3) = 5 gals of material. Some joints might take more grout; some might take less depending on the soil type and the void space in the soil. This formula works for any of the acrylic family of products: acrylamide, NMA acrylic and acrylate.
According to the white paper published by the Infiltration Control Grouting Association (ICGA), a division of NASSCO titled “Overview of Lateral and Main/Lateral Connection Lining and Sealing Technologies,”, there are seven rehabilitation approaches to consider when evaluating how to repair lateral pipe. These include variations on lining, grouting and pipe bursting.
The optimum technology is dependent on a proper assessment. Decision-support criteria begins with the answer to this question: “Is a structural repair required?” If the answer is yes, chemical grout is not optimum. If the answer is no, chemical grout is the most cost-effective, long-term solution. The U.S. Department of Energy performed a 20-year study on seven different grout types for the containment of hazardous waste and determined acrylamide grout has a 362-year half-life in the soil.
The engineering, municipal and contracting communities are advocates of the trenchless industry. You can find the white paper mentioned above, as well as performance specifications and other valuable resources on sewergrouting.com.
Weighing short-term cost and long-term benefits, chemical grouting is a top consideration for sealing structurally sound laterals and lateral connections. Understanding the 4Ps provides insight as to why.
This article was written by the NASSCO Lateral Committee.