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| The reinforced concrete pipe was removed, cleaned and reinstalled. |
By Peter O'Connor and Serge Poirier, Centennial Concrete Pipe & Products Inc., Ottawa
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| The reinforced concrete pipe was removed, cleaned and reinstalled. |
When reinforced concrete pipe is specified, it is due to its service life and performance characteristics. Concrete pipe drainage systems are expected to be installed on projects that have decades-long design lives, often extending for more than 100 years. Rarely is a concrete pipe system prematurely excavated with replacement in mind. A recent project in Gloucester, near Ottawa, Ontario, is a reminder that reinforced concrete pipe can be reused.
Some contractors in the Ottawa area are familiar with recycling concrete pipe systems. In 1998, 110 metres of a 33-year old (1090 mm x 1725 mm) horizontal elliptical pipe was exhumed, cleaned and re-installed on a site that had been contaminated by coal tar. The system was upgraded with gaskets and maintenance holes when it was re-installed.
In 2000, a situation similar to the one in 1998 occurred where C.A.C.E. Construction (1991) Ltd. started soil clean-up of a contaminated site at Innis Road and Cyrville Road in the City of Gloucester. The contract included the removal of approximately 45 metres of a 1,350 mm diameter storm sewer installed in 1975. Soil around and under the pipe was contaminated with hydrocarbons, and had to be removed and replaced. The contractor suggested that the existing pipe should be reused, if found to be structurally sound.
After a few pieces of the pipe had been excavated, John Landerville of C.A.C.E. realized that the system appeared to be in excellent condition. He contacted City officials and Centennial Concrete Pipe who had supplied the pipe, and requested strength tests to determine if the pipe could be reused for the storm water drainage system.
The pipe had been installed in a 2.44 metre (8 feet) wide trench with a bedding of clear stone, and a distance from the top of the pipe to finished grade of 2.55 metres (8 feet, 6 inches). The new trench for the installation would be 4.5 metres (15 feet) wide with granular C bedding specified, and the pipe would be buried under 2.6 m (8.5 feet) of fill. Greater loading on the pipe was due to the greater trench width, necessitated by removal of contaminated material.
The test to determine concrete pipe strength is called the Three Edge Bearing Test, with results referred to as the D-Load of the pipe. A piece of pipe is placed under extreme loading until a 0.3 mm crack appears in the wall of the pipe. At this point, a reading is taken of the force that was required to cause the crack. The pipe can then be subjected to greater forces until it fails. Another reading is taken at this point and reported as the ultimate load for that production line of pipe.
The piece of pipe delivered to the Centennial test facility was a 2.44 m long, 1,350 mm diameter 100 D with an O Ring gasket. The table shows the test results undertaken on November 14, 2000.
Serge Poirier, Centennial's Plant Superintendent, reported that the D-Load of the pipe supplied from the job site met the requirements of 195D. The pipe had actually strengthened from 100D to 195D while buried over the 25-year period. The Centennial report noted that the entire pipe run could be considered to meet the same requirements of 195D structural strength based on the following assumptions:
The report went on to suggest that, with regards to the new installation conditions of 2.6 metres of fill and a C Bedding, a 65D pipe would be sufficient. The report concluded that the pipe would be more than adequate for reuse on the job.
Only six pieces of new pipe had been installed before the testing was requested. Once the results were accepted by the City and consulting engineer, Golder (Montreal Office), the old pipe was carefully removed, steam cleaned, fitted with new gaskets and re-installed.
The contractor benefited from the re-use of the pipe because they were able to continue working on the site clean-up with an immediate supply of high quality concrete pipe. The technique was so successful that the contractor is expected to clean up another section of the area early in the new year, reusing the existing precast concrete drainage system. Only pieces broken during excavation will be replaced with new concrete pipe.
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