Chemical Sewer Grouting
Chemical Grouting Of Sewer Lines
Chemical grouting of sewer mains to control groundwater infiltration and exfiltration at joints and connections has become the mainstay of many sewer system maintenance and rehabilitation programs. The chemical grouting process is more than 40 years old and lateral grouting has been done for the past 20 years, demonstrating an effective method for stopping groundwater entry at these recognized infiltration entry points.
Chemical grouting is not a structural rehabilitation method for
a wastewater collection system. Chemical grouting is a method
of preventing ground water from entering a collection system through
failed joint connections of structurally sound pipe.
What Is I & I - Inflow and Infiltration
Inflow & Infiltration is the unwanted entry of groundwater into a sewer collection system. While posing no harm to the sewer collection system, the groundwater entering the sewer becomes contaminated and along with the sewerage must be treated. Thus, the groundwater becomes an unnecessary burden and cost to sewage treatment plants. Added groundwater also reduces the capacity of the collection system to carry "pure" sewerage. All sewerage treatment plants experience higher than normal flow rates during rain events, these high flow rates in part can be contributed to inflow & infiltration on non-combined (sewer & storm) collection systems.
Test & Seal of Sewer Line Pipe Joints
Grouting of sewer line joints is also known as "Test & Seal". The procedure is done using specialized equipment with the main component known as a packer. Using CCTV equipment, the packer (connected to the gout truck with 4 hoses) is positioned at the pipe joint. The operator inflates the packer forming an air tight seal on each side of the joint. When inflated, the operator sends pressurized air to a open port located in the middle of the packer & exposed to the singular joint. If the pressure holds, the joint is sealed and not leaking. If the pressure test fails, the operator injects an amount of grout under pressure to seal the joint and then the air pressure is repeated. Air pressure tests and grout injections are repeated until the joint passes the air pressure test. It should be noted chemical gout does not form a seal between the two pipes, grout forms a seal on the outside of the pipe utilizing the surrounding soil as part of the joint seal.
Chemical grouting is not a joint and crack filling or cementing process. Instead, two water-based chemicals are mixed and injected under pressure at the point of sewer joint failure or infiltration entry. Under pumping pressure, the grouting chemical mix passes through the sewer joint, crack or into the annular space between old pipe and new liner at the service cut out and into the annulus and surrounding soil with back fill materials filling the soil voids and displacing the groundwater. The chemical grout mix rapidly gels in the annulus and adjacent soil, effectively stopping the flow of groundwater. The sewer pipe backfill and pipe bedding soil on the outside of the sewer in the area of the leak is stabilized because the groundwater is no longer flowing into the main and carrying fines into the sewer system. The injection and sealed soil volume exterior to the pipe can often be very large compared to the pipe displacement. Joint leak sealing in 8-in. pipe can take 0.5 to 2 gals of chemical grout, and with 20 percent water to soil material void volume, this amount of grout seals 2.5 to 10 gals of soil around the leak. This large grout ball or soil mass further impedes groundwater flowing outside the old sewer main in the pipe bedding materials.
Chemical Grouting of Sewer Laterals
Using a lateral grout packer, chemical grouting of laterals and the lateral connection can be achieved. The chemical injection packer used for lateral grouting forms three seals within the lateral connection structure. The main is blocked off on each side of the lateral connection and a third plug is concurrently inflated up the lateral line to a predetermined distance from the main (normally 1 to 8 ft but occasionally as much as 15 to 30 ft) to seal off the lateral connection. Once the packer is positioned in place, the bladders are inflated and the lateral pipe and connection are isolated for the "Test & Seal" procedure to begin. The same procedure is used for laterals, an air test is performed and if there is a failure grout is injected and the test is repeated until the joints pass the air test.
|
|