Drainage system inspection affirms ADS pipe performance
Advanced Drainage Systems (ADS) engineers recently examined hundreds of feet of ADS high density polyethylene (HDPE) pipe, part of a stormwater drainage project installed in 1987 in the popular resort town of Ocean City, Maryland. Remote video, hands-on inspection and a laboratory test were used. This look back on the twentieth anniversary of the project provided documentation of the pipe's long-term performance in terrain not known for being "pipe-friendly" according to ADS' Mike Freshwater...
• ADS inspects first large scale HDPE pipe project and finds the 1987 installation in excellent condition in demanding seawater and sand region
OCEAN CITY, MD, March 11, 2008 -- Advanced Drainage Systems (ADS) engineers recently examined hundreds of feet of ADS high density polyethylene (HDPE) pipe, part of a stormwater drainage project installed in 1987 in the popular resort town of Ocean City, Maryland. Remote video, hands-on inspection and a laboratory test were used. This look back on the twentieth anniversary of the project provided documentation of the pipe's long-term performance in terrain not known for being "pipe-friendly" according to ADS' Mike Freshwater, the original ADS representative for the project.
"The inspection definitively concluded that after the initial 20 years of service life, the ADS N-12® HDPE pipe installed in Ocean City is still performing as originally designed with no visual signs of deflection or other defects," said Nathan Jovanelly, ADS regional engineer. "In addition, lab results from tests performed on samples taken showed that the exposed sections at the outlets have incurred no UV degradation as a result of constant exposure to the sun."
In the 1980s, the Maryland State Highway Administration began a series of projects to enhance pedestrian safety, create landscaping and improve drainage on Route 528, the major north-south highway running along the Atlantic Coast in Ocean City.
"The east/west flow of water during storms was a traffic hazard, and therefore, drainage was a major component of the design," according to Freshwater.
The popular resort town located on a barrier island near the Maryland-Delaware border sees road traffic skyrocket from 10,000 vehicles a day in the winter to ten times that during the summer.
Construction began in the fall of 1987 after the rush of the tourist season ended. More than 16,500 feet of ADS N-12® HDPE pipe, ranging from 12" to 24" diameter, was installed. HDPE was selected for its smooth interior and corrugated exterior, which provides excellent hydraulics and structural strength.
"It was imperative that the pipe have a superior joining method and would also be able to keep water flowing with a minor slope because some areas had less than a three degree down run. The outlet elevations of the storm sewer system were calculated to be equal to the low mean tide," Freshwater explained.
Ocean City is a beach with most areas being just three to four feet above sea level. Once buried, the pipe would be in contact with seawater and be subject to shifting that would affect the pipe's joint connections. Also factored in were the 100,000 plus vehicles that would travel this road every day during the summer. The ADS HDPE pipe was selected because it stands up to a wide range of corrosive environments and maintains its joint integrity. "This is what we set out to confirm during our inspection two decades after the installation. We found the pipe was in good condition with no evidence of infiltration," Freshwater stated.
According to Steve Drumm, assistant bureau chief, bureau of highway design for the Maryland State Highway Administration, in a July 1988 PUBLIC WORKS article, concrete pipe was not selected because past experience demonstrated that concrete pipe laid in the area's sandy soil misaligned, which eventually caused erosion of the overburden.
Steel pipe was also set aside because it had a history of corrosion due to salt water standing in the pipe during half of every day because of the tidal action. The corrugated ADS HDPE pipe with a smooth interior was ideally suited for the flat-grade issues presented in the design, according to the magazine's article.
In June 2007, Jovanelly and Freshwater inspected the infrastructure from 41st Street at the Convention Center to 59th Street (the parameters of the original contract). Inspection criteria included visual observations, hand measurements, and a high-tech zoom inspection camera. The camera unit required a collapsible pole, 216:1 color-zoom video camera, high-intensity spotlights so the inspection could be done primarily at night to take advantage of reduced traffic levels, and a recording system that was battery operated. The Quickview™ camera has the technology to take both still photos and digital video footage. With underwater capability, the Quickview was also well suited to the often wet conditions of the inspection.
With the help of the Ocean City Police, much of the inspection occurred from 3:30 a.m. and 6:00 a.m. The high ADT loadings logged prohibited lifting storm sewer grates in the daytime. Even at the early hours a police escort was required because buses run every five minutes, twenty-four hours a day between Memorial Day and Labor Day.
The inspection criteria included visual signs of deflection, pipe degradation, and/or any other defect that might potentially affect the performance of the pipe. Most of the inspection was done with the Quickview™ camera. Whenever possible, however, the pipe was also viewed without the camera to verify results obtained from the unit. Although it was not required as part of the inspection criteria, sediment amounts and other maintenance issues were recorded.
The initial inspection took place at 41st Street near the Convention Center where inlet grates were lifted for video inspection of the dual 15-inch diameter pipes. This initial installation was encased in concrete, and no deflection was found. The pipe liner was in good condition and little sediment was found. The inspection in this vicinity included one inlet and pipe run installed by the Ocean City Department of Public Works. Because the pipe was installed under the loading docks and is subject to almost daily tractor trailer loading, it was also inspected and recorded. Further downstream, the 15-inch pipe continued to perform well through to the outlet at the Isle of Wight Bay.
The subsequent pipes were installed as cross pipes that drain stormwater to the central box culvert collector in the center of Route 528, also known as Coastal Highway. These pipes were installed at minimal slope with 12 inches to 24 inches of cover. The cross pipes are at 48th and 49th Streets, 52nd to 54th Streets, and 56th, 57th and 59th Streets. Local landmarks such as hotels or gas stations were also used as reference points. According to the original design engineer, Doug Moyer, P.E., Johnson, Mirmiran and Thompson Engineers, all pipes were to be installed with the design minimum of 95% compaction of the native sand backfill material.
Each of the cross pipes inspected are subject to the same HS-25 loads and have almost the same pavement section. Because in the summer months the ADT loadings are excessively high, these pipes were selected for the inspection. After the pipe evaluations were completed, all pipes inspected were found to have no defects that would affect the long-term performance of the pipe.
Additionally, a sample for laboratory testing of HDPE pipe continuously exposed to sunlight was taken from the 53rd Street installation at the outlet bulkhead in the lagoon leading to the bay. Lab results showed that after 20 years of exposure the pipe contained no signs of damage due to UV rays and that the pipe meets the AASHTO M-294 resin requirements that were current at the time of installation.
Since the 1987 installation, millions of feet of ADS N-12 HDPE pipe have been installed in major highway drainage projects throughout the United States.
Advanced Drainage Systems Inc. (ADS) is a producer of HDPE corrugated plastic pipe. Founded in 1966, it serves the stormwater drainage industry through a global network of 42 domestic and international manufacturing plants and more than 30 distribution centers.