Much of our nation’s underground infrastructure is reaching or functioning beyond expected lifespans. This critical network of pipes and mains serves our most basic water and sanitary needs. Many municipalities are faced with the challenging task of replacing or lining deteriorating facilities while minimizing service disruptions for residents and businesses. KCI recently completed a successful pilot to replace 830 feet of water main in the city of Bowie, Maryland, using pipe bursting. Although this trenchless approach is used frequently to replace sewer lines, this project offered proof of concept for upgrading and replacing aging city’s water network.
Pipe bursting is regularly used to replace sewer mains, but water lines can present additional challenges including valves, fire hydrants and service connections.
John Blondell, PEEnvironmental Engineer
The city of Bowie owns and operates a water and sewer utility system that serves 7,800 residents and 100 commercial businesses. The system, which was installed in the 1960s, includes approximately 90 miles of water distribution piping. While the 10-inch and larger pipes are concrete-lined cast iron, most of the piping is six or eight-inch diameter, unlined cast iron pipe, which has experienced significant corrosion problems. The most common is tuberculation, which is the formation of small mounds of iron oxide (tubercles) inside the piping. Tuberculation accumulation over the past 50 years has reduced the hydraulic capacity of the pipes, and when high flows are experienced, suspended iron oxides discolor the water.
After investigating different strategies to replace their water mains, the Bowie Department of Public Works initiated a prototype pipe bursting project in one of the neighborhoods experiencing very low flows. This particular section of six-inch main is approximately 830 feet long and serves 23 homes that are not supplied by any other water mains. The water main extends beneath trees, asphalt roadways, paved driveways, sewer and gas easements, and a stream.
KCI recommended utilizing pipe bursting to replace the main, noting that the approach would limit excavation, thereby reducing cost, shortening the construction schedule, and minimizing impacts to property owners. The design effort was able to be streamlined as well. Since pipe bursting is a means for rehabilitating existing pipe in the same location, the design drawings could be produced without the need for a full topographic survey, which is required for standard pipe replacement engineering drawings. The design utilized the existing city GIS mapping as a basis for the construction plans to indicate the location of the bursting efforts, as well as other accompanying details. One particular challenge faced by the design team was the lack of a profile drawing for the existing water main. The profile would have indicated the water main depth as well as the configuration of the water main beneath the existing stream. Because of this, the design team undertook several test pits at the stream crossing to verify the absence of pipe fittings or concrete encasement, which would potentially prohibit the bursting head and pull rods from passing through this area.
This method has been used for more than 30 years for replacing sanitary sewer pipes, but more recently is being employed for water main replacements. The success of this project offered proof of concept for replacing the city’s aging water distribution system while minimizing disturbance to the daily activities of the residents. In Bowie, this pipe bursting project proved successful with numerous benefits including:
Reducing design and construction cost by approximately 40 to 50 percent
- Shortening design and construction durations by between 4 to 6 months
- Limiting pavement disturbance
- Lowering the risk of damage to adjacent properties and nearby infrastructure
- Minimizing environmental concerns and permitting associated with the stream crossing
Like many approaches for upgrading or replacing underground infrastructure, pipe bursting may not be appropriate in all locations and must be evaluated versus other methodologies for constructability, efficiency and cost effectiveness. For the city of Bowie and many other municipalities, it is another tool in the toolbox in managing their aging assets and providing the best level of service possible to their customers.