By resurrecting a once-popular system of pipeline sealing and using it in conjunction with a new method of manhole coating and sealing, an engineer/contractor team has eliminated more than 30 percent of total inflow and infiltration for a southside Chicago suburb.
Working under guidelines of the Illinois State EPA, Cook Countys Metropolitan Water Reclamation District, Akhras Associates Inc., and National Power Rodding Corporation, have combined forces to clean, televise, test and reseal 250 defective manholes and all 70,000 linear feet of piping within Ford Heights, a community of 4,600 originally built around a Ford Motor Company stamping plant.
The older repair system, joint grouting, took care of the pipeline problems at a fraction of the cost and equal or greater life expectancy than point repairs and newer repair methods, the consultants said.
The new system, spray-on polyurea, applies a seamless highly resistant elastomeric coating. This coating adheres positively to all surfaces, effectively stopping manhole leaks.
The consultants expected an inflow/infiltration (I/I) Corrective Action Plan target limit of 20 percent, but the two programs together left only 12 percent of the original I/I.
All sewer lines in the community are again flowing freely, according to Salem Akhras, P.E., vice president and project manager for Akhras Associates.
Basement and street backups related to sewer line problems have been greatly reduced and possibly eliminated, said Saul Beck, Ford Heights mayor.
Clean and Televise Lines
The first step in the remediation procedure was for contractor specialists to clean each sewer line. This task was accomplished by running a high-pressure jetter hose and nozzle through each successive manhole-to-manhole section. One or more passes at water pressures up to 2000 psi cleared deposits from pipeline segments ranging from 200 to 500 feet long (and averaging 280 feet).
Clean and Televise Lines
Following this cleanout step, the same equipment was used to thread a 3/8-in. cable through the line; the cable initially was used to control movement of a closed-circuit television camera. Its pictures would be used to check pipeline soundness. Narrated videos, together with a still photo of each problem area, provided a permanent record of the lines.
Clean and Televise Lines
Wall materials ranged from clay, concrete and ductile iron to ABS and PVC plastic. The pipes were installed mostly in the 1950s. Review of this evidence by an engineering team revealed that the wall materials contained no breaks or cracks.
Clean and Televise Lines
The joints were a different story. Located every 2 to 5 lineal feet, at depths of 4 to 29 feet, a majority of joints showed signs of infiltration. As it turned out, about 75 percent - an estimated 184,000 of the towns estimated 245,000 pipeline joints servicing about 53,000 of Ford Heights total linear feet - needed repair.
Pressure Testing, Grouting Follow
Once the studies were completed and priorities established, National Power Rodding crews returned to the field and to the same in-line cables. This time, a contractor-owned grouting machine was attached to the cables and the equipment was routed through the same sections of piping which had been cleaned and viewed.
Pressure Testing, Grouting Follow
Grouting itself started with the application of a pressure test to each joint. Pressure applied was equal to a specified intensity but not less than one half pound per foot of depth. Typical pressures ranged around 8 psi.
Pressure Testing, Grouting Follow
If the tested joint withstood the pressure, the joint was considered sound and the pressure-testing/grouting equipment moved on to the next joint.
Pressure Testing, Grouting Follow
If the joint failed the test, the grouting machine was cabled into position per images shown on the television screen. Remote controls inflated the end diaphragms of the grouter to isolate the problem. Positive-displacement proportioning pumps then forced chemical grout into all openings. Made of two newly-formulated liquids, acrylamide grout and ammonium persulphate activator, the material filled voids in and outside the joint. In less than a minute, a permanent gel resulted, sealing the leak(s).
Pressure Testing, Grouting Follow
Once its effectiveness was proven, end elements of the grouting machine were deflated and the unit moved down the pipe 2 to 5 feet to the next joint where operations were repeated.
Pressure Testing, Grouting Follow
Like other work in the line, each move and each joint grouting were continually monitored via the screen in the contractors vehicle.
Pressure Testing, Grouting Follow
This procedure continued at a rate of about one 280-lineal-foot manhole-to-manhole section per day, depending on size of pipe and number of defective joints. Cycles averaged around 5 to 10 minutes per defective joint, including positioning, inflating the diaphragm, air-testing, grouting, retesting and deflation.
Pressure Testing, Grouting Follow
Grouting portions of the project were completed in four months, on schedule and within budget.
Pressure Testing, Grouting Follow
In the cleaning process, sand, solids and other debris flushed down the lines and was lifted out of the manholes to be taken to landfills. No stone, silt, wood or other materials were flushed into the system.
Manhole Rehabilitation
The contractors did most of the work, leaving the city only the planning, locating and exposing manholes, and inspection of them. Safety was emphasized continually. Outside air was constantly supplied from OSHA-approved positive-pressure pumps to the manhole interiors. Workers there and on the surface all wore such protective clothing as Tyvex suits, gloves, steel-toed boots and full face masks to eliminate risks of contact exposure. Procedures and personnel met or exceeded safety application standards and attained levels of safety efficiency recommended by the supplier.
Manhole Rehabilitation
The rehabilitation started with the cleaning of all interior manhole surfaces. Dirt, scale, and algae were removed by contractor specialists; so were mineral deposits, efflorescence, grease and other contaminants. In most cases, hose water applied at 2000 psi did the job. Chemical cleaning and sand-blasting supplemented the high-pressure water. Cleaning of the 250 manholes averaged less than 1 hour each.
Manhole Rehabilitation
The technicians then patched cracks, holes and other obvious sources of water infiltration and inflow. A number of repair methods were used, including sealing by the same type of pressure grouting used in the pipelines, physical replacement of missing and damaged bricks and broken adjustment rings, filling cracks and holes with such non-shrink materials as polymer modified concrete and resins.
Manhole Rehabilitation
Rusted metal frames, steps and other non-concrete parts, previously cleaned by sandblasting, were similarly repaired or replaced as required.
Manhole Rehabilitation
In a final step before using the new sealing material, high-pressure washing with ordinary hydrant water scrubbed the surfaces; blown air dried them. The crews checked to make sure the pH of the surfaces ranged from neutral to slightly alkaline, per ASTM Specification D-4262.
New Sealing Material
Next came spray application of a liquid primer which increased adhesion of the new polyurea material.
New Sealing Material
Spraying the polyurea over the entire manhole interior surface completed each rehabilitation. For this task, one member of each two-person crew worked from the manhole bottom to the top. One side of his two-component dispenser fed the polymer, and the other fed the resins. The combination, applied by hand-held hose, formed a homogenous, seamless coating at least 125 mils (1/8 in.) thick; more over areas of major damage.
New Sealing Material
The manholes were roughly 10 feet deep and 4 feet in diameter. The entire coating step took an average of only 35 minutes per manhole. Dry to the touch in less than 20 seconds, the coating naturally cured to its desired hardness and clean white color in less than 24 hours. The surfacing conformed over all geometric shapes inside the manholes.
New Sealing Material
"Final adhesion was complete," said Akhras. "Every manhole surface was sealed - cement block, brick, block, mortar, adjustment rings, everything. "This rehab method cost a fraction of the replacement cost."
New Sealing Material
"Final adhesion was complete," said Akhras. "Every manhole surface was sealed - cement block, brick, block, mortar, adjustment rings, everything.
New Sealing Material
"This rehab method cost a fraction of the replacement cost."
New Sealing Material
And costs have remained low, because the polyurea coatings have stayed intact. The coating has shown the ability to absorb and dissipate the stresses of thermal cycling, traffic impacts, and direct hits of snowplow blades.
New Sealing Material
Its wide formulation flexibility allowed National Power Rodding to technically engineer varying polymers with properties to fit differing parameters.
New Sealing Material
"The new material has proven much more durable," Akhras said. "Being somewhat elastic, it absorbs the stresses of our frequent freeze-thaw cycles which often break cement bonds, generally within one year."
