A variety of chemical grouting systems are available on the market today to seal leaks and stop infiltration and exfiltration in sewer systems. Most leaks in structurally sound sewers are through pipe joints, manholes, service connections, and the first few feet of service laterals.
Chemical grouts do not stop leaks by simply filling cracks. They are forced through cracks and joints and gel with the surrounding soil, forming a waterproof collar around leaking pipes and manholes. The gel collar adheres to the outer surface of the pipe and will stay there unless removed by excavation. The maximum life expectancy of properly mixed and placed grout is not yet known, but samples have been examined after 30 years and found to be in “like new” condition.
If humidity in the soil declines for a long period, the grout may begin to dry. However, when the soil humidity returns, the grout absorbs moisture and returns to its original condition. Line flow and soil humidity around leaking manholes and sewers are almost always high enough to prevent any significant grout shrinkage. Additives which prevent shrinkage may be used where dryness could be a problem.
Application
In man-entry pipelines, chemical grout is usually applied via manholes with hand-held equipment. However, for small diameter (24-in. and less) pipes, all testing and sealing operations must be performed with remote-controlled equipment. A device called a test/seal packer is used to pressure test joints to determine whether they are watertight. The packer is also used to seal any joints which fail the pressure test.
Application
Chemical grout should not be used for structural repair. If a pipe is badly cracked or damaged, the inflatable packer can cause additional damage. Joint testing and sealing cannot be performed effectively in a pipe which has roots, debris on the invert, excessive roughness, cracks, breaks, severely offset joints, or other conditions which prevent the inflatable ends of the packer from making continuous, tight contact with the pipe on each side of the target joint.
Equipment
Basic test/seal equipment consists of:
- Closed-circuit TV system to locate the packer over the pipe joint.
- Test/Seal packer.
- Control panel to control a power winch, TV camera, packer inflation, joint test sequence, chemical injection, and to record data and view the operations.
- Hose and reel system to deliver air and chemicals to the packer.
- Chemical tanks, pumps, air and electric systems.
- Remote-controlled winches.
Equipment
The design of test/seal packers varies from one manufacturer to the other, but all share certain characteristics. Mainline packers are cylindrical and can be positioned in a pipeline by cables attached to each end. They have inflatable ends which can be expanded to isolate a short length of pipe and create a void into which either air pressure or chemical grout can be pumped. Most are hollow to permit some sewage flow when the packer is inflated.
Equipment
Lateral packers have additional equipment which allows them to insert a device into lateral lines to seal the lines while they are pressure-tested and sealed with chemical grout.
Grout Types
There are four major types of chemical grout which are commonly used to seal manholes, sewer pipe joints, service connections, and the first few feet of service lines:
- Acrylamide
- Acrylic
- Acrylate
- Urethane
Grout Types
Acrylamide is a monomer and the others are all prepolymers. After curing, all of the polymers are non-toxic, stable, inert, and permanent when used below grade.
Grout Types
Gel grouts have a viscosity similar to water when they are applied. As a result, they pass through cracks and other openings in pipes and gel very quickly. In neat form, cured gels look like stiff gelatin or rubber. In actual use, they penetrate the soil outside the pipeline and form a gel/soil matrix that is impermeable to water.
Grout Types
Urethane foam grouts are important in sealing treatment plant structures and manholes in sanitary sewers. They are also used to seal pipe joints in storm sewers and to fill the annulus at the manhole after slipline installations. They are seldom used in small diameter sanitary sewers. The flexible urethane foams create a seal in cracks and joints, as opposed to forming a grout collar on the outside of pipes.
Barrel Test
Since much of the chemical grout installation takes place out of sight, operators should make sure their installation and test equipment is in good working order by conducting an above-ground barrel test at the beginning of each work shift and at other random times.
Barrel Test
The National Association of Sewer Service Companies (NASSCO) has developed a control test (Barrel Test) which they recommend. A test cylinder is constructed to simulate the barrel of a sewer pipe. It should be set up so that the pressure readings on the test cylinder gauge and the void pressure monitoring gauge can be observed together during the test. The reading on both gauges should be the same throughout the test. This test will also verify whether or not the packer is capable of holding adequate pressure under ideal conditions.
Barrel Test
During the test, the packer sleeves are inflated to the pressure recommended by the manufacturer. Then, the test medium (either air or water) is injected into the packer void until the maximum pressure used to test the actual pipe joints is reached. This pressure should be held for at least one minute to verify that the packer will hold pressure. After one minute the shutoff valve should be opened to simulate a leak. Both gauges should quickly return to zero. It is recommended that this test be repeated at least three times.
Pipe Wall Control Test
A structurally sound section of pipe which contains no joints or lateral connections should be tested to establish the maximum performance of a good joint. This test will also demonstrate whether the packer can maintain the void pressure necessary to properly test and seal pipe joints.
Pipe Wall Control Test
The packer should be positioned on a sound section of sewer pipe which has no joints, cracks, or incoming lines. Then, the packer sleeves should be inflated to the pressure recommended by the manufacturer and held for one minute.
Pipe Wall Control Test
If the void pressure cannot be held, grout sealing will not be effective because the grout will leak past the packer sleeves instead of being forced through cracks. Since no joint can possibly test better than a sound section of the pipe itself, the reason for the failure must be found and corrected before work begins. Some possible reasons the test may fail:
- Debris on the pipe invert
- Roughness of the pipe
- Porosity of the pipe
- Leaking fittings or hoses on the test/seal equipment
Test Joint
After testing, the packer can be moved to the first pipe joint or lateral line connection. A joint or connection that is actively leaking need not be tested; the sealing operation may begin immediately. All joints, cracks, and incoming lines should be tested. To properly test a joint, the following steps should be taken:
Test Joint
The packer must be centered on the joint or lateral connection. Verify that the packer manufacturer’s alignment instructions are being followed. The packer sleeves should be expanded until they make circular contact with the pipe on both sides of the joint or connection to be tested, then inflated to the pressure recommended by the manufacturer.
Test Joint
As the packer sleeves are expanded to press and seal against the pipe, one of the following conditions will result:
Test Joint
- Void pressure may increase because the volume has decreased due to the expanding packer sleeves and there is no leakage from the void.
- Void pressure may increase until it equals groundwater pressure due to infiltration into the void. Unless care is taken, one could mistake the steady pressure as an indication of a good joint.
- Void pressure may decrease or show no change because there is leakage past the packer sleeves or through the pipe joint.
Test Joint
Testing is usually performed by pumping a test medium (liquid or air) into the void and monitoring the resulting void pressure. In other cases, testing may be performed by expanding the center section of the packer to compress the air and the water trapped in the packer void when the packer sleeves were inflated. In either case, it is necessary to develop a void pressure greater than groundwater pressure outside the pipe in order to tell whether or not the joint is leaking.
Test Joint
If the required test pressure cannot be developed, the joint will have failed the test. If the required test pressure can be developed, the flow of the test medium may be stopped. If, in the case of a liquid test, the pressure cannot be maintained for one minute with less than 1/4 gpm flow, the joint will have failed the test. If, in the case of an air test, the void pressure decreases by more than 2 psi within 15 seconds, the joint will have failed the test.
Test Notes
The manner in which pressure in the packer void changes during a test depends upon several factors:
Test Notes
The test medium: Water and air perform very differently when used as the test medium.
Test Notes
- Air will be above the water in the void, unless it leaks out.
- Air escapes through a small hole so easily that a leak which is too small to seal effectively with chemical grout can be detected. A leak of the same size may pass a water test.
- If water is present in the packer void, it will always be at the bottom of the void.
- Water cannot be compressed. In theory, if one drop leaks out of a fixed volume, all pressure is lost.
- Water creates its own static pressure. Water in a hose that is connected to a pressure gauge 23 feet below will create a static pressure head of 10 psi at the pressure gauge. Therefore, packer void pressure must be measured at the void and the information must be transferred by some means other than a hose filled with water.
Test Notes
The location of a leak: There can be a significant difference in test results depending upon whether a leak is located at the top or at the bottom of the packer void, and whether the test medium is air or water.
Test Notes
- Air test, leak at the bottom of the packer void: Air goes to the top and will push water out through the bottom leak. The leak is tested with water until air fills the packer void; then pressure will fall quickly as the air escapes through the leak.
- Water test, leak at top of packer void: Water will push air out through the leak until the packer void is filled with water; then the pressure may rise.
- Air test, leak at the bottom of the packer void: Air goes to the top and will push water out through the bottom leak. The leak is tested with water until air fills the packer void; then pressure will fall quickly as the air escapes through the leak.
- Water test, leak at the bottom of the packer void: Pressure may rise at first, then begin to slowly fall after water source is cut off.
Joint Sealing
If the joint passes the pressure test, that fact should be noted on the records and the packer moved to the next joint or lateral connection. If the joint fails the test, it should be sealed. The sealing process involves the following:
Joint Sealing
- Pump the grout chemicals into the packer void. The two parts of the chemical grout system may be pumped through hoses from the chemical tanks to the packer void by either pressurized air or mechanical, positive displacement proportioning pumps. In either case, the two grout components must be pumped in a correct ratio of base material to activator. They must also be adequately mixed in the packer void or the chemical grout will not form properly.
- Grout injection should be terminated when void pressure approaches 10 psi. If 10 psi is not reached rather quickly, pumping should be stopped for a period at least equal to the duration of the grouts gel time. At that point, additional grout may be pumped. If the pressure has not begun rising after pumping additional grout, it may not be possible to seal the leak. In this event, the client’s inspector and the grout operator should decide if another attempt should be made. In this situation, the opinion of an experienced operator is usually correct.
- The packer sleeves should now be deflated. The void pressure may drop to minus 2 psi and then return to 0 psi. The deflating packer sleeves often create a vacuum before they lose their seal against the pipe surface.
Joint Sealing Verification
After a leak has been sealed, the packer should be deflated and moved. This will break up the gel ring around the packer and cause the void pressure meter to return to zero. If the void pressure does not return to zero, the contractor should clean and/or adjust the equipment so accurate void pressure readings can be made. Then, the leak should be tested again. Leaks that fail to meet the specified test criteria should be resealed and retested until the specified test criteria can be met.
Residual Sealing Material
Residual sealing materials that extend into the pipe reduce the pipe’s diameter and restrict flow, so they should be removed. Sealed joints should be left reasonably flush with the existing pipe surface. If excessive grout accumulates in the pipeline, the pipe section should be cleaned to remove the residual material.
Records
The installation contractor should keep the following records for each job:
- The identity of each manhole-to-manhole section where work is done.
- The location of each joint, crack, or incoming lateral line that was tested. The pressure used should be recorded as well as the result.
- The location of each joint, crack, or incoming lateral line where grout was applied, how much grout was injected, and whether or not the joint was sealed.
- The exact identification of the grout that was used.
Warranty
Grouting specifications often include provisions for an 11th month inspection of at least 10 percent of the total joints tested in the original contract. The line sections to be re-tested should be selected at random by the owner and should represent the same mix of sizes as the original contract. All joints in the selected lines must be re-tested and any joints which fail must be resealed at the contractor’s expense. If 5 percent or more of the tested joints fail, the contractor must continue to test and seal until at least 95 percent of the total joints tested pass the test. By making these tests during the 11th month, the quality of the job may be verified before the warranty expires.
