Waterline Replacement through Pipe Bursting in Greensboro, N.C.

While operating their family-owned sewer cleaning and rehabilitation business, brothers Jeff Greene, P.E., and Marty Greene have found a growing need for the use of pipe bursting.
   
Pipe bursting is a viable alternative to traditional dig-and-replace construction. More cost-effective, expedient, less disruptive to adjacent services and quieter than open-cut methods, the pipe bursting process is especially ideal for congested areas such as cities, municipalities and even manufacturing or industrial plants.

KRG Utility has developed a relationship with the City of Greensboro, N.C., replacing its deteriorated gravity sewer lines since 1998. During this time the city has realized the benefits of the utilization of pipe bursting and sliplining. These rehabilitation methods are equally beneficial when updating municipal water systems.

Much of the City of Greensboro’s water system is more than 70 years old, having been constructed from the 1920s and forward. Additionally, much of the older water system is located in congested, high-traffic areas such as downtown and major thoroughfares. Because the majority of the system is cast iron pipe, the City has relied on traditional methods of water line replacement, which in these congested areas becomes problematic and inconvenient.

Perhaps no other story captivates the importance and urgent need for replacing old water line than the story of Wendover Avenue in Greensboro.

Every city has at least one road “bad traffic area,” where the slightest hiccup brings everything to a screeching halt. Utility departments dread the thought of routine maintenance, much less emergency repairs, in these areas because of high traffic, difficult surroundings, safety concerns and the inevitable citizen complaints. Wendover Avenue is such an area for the City of Greensboro.
 
When the call came from the police department that there was a car-size hole in Wendover Avenue, the Department of Water Resources was quickly on the scene. Luckily, the person who drove into the hole was not injured.

The image below shows the magnitude of the failure. What this image does not show is how quickly the failure occurred. To give an idea of how quickly the hole manifested, a police officer had just driven over this spot and felt a “bump.” Before he could turn around to investigate, the roadway had collapsed and “eaten a Honda.”

The culprit for the collapse was a 12-in. cast iron pipe installed in 1929 that had fractured, causing the dramatic failure. After dealing with the immediate emergency of the failed section, the Department of Water Resources initiated the design for a traditional dig-and-replace project. Approximately six months later with a budget estimate of $1.3 million, the City chose to investigate using pipe bursting to replace the pipe. The success of the project was extremely important with all eyes from City elected officials to news crews reporting constantly of progress and inconveniences. What would have been a high-profile project based solely on location became even more sensitive.

The initial capital improvements project included replacing approximately 3,000 ft of 12-in. water line. This included 3,000 ft of three-lane overlay on Wendover Avenue required by N.C. Department of Transportation because of the number of cuts required for the installation.

To avoid the cost and disruption of the asphalt overlay, the City chose to install 1,400 ft of 4-in. fusible PVC via directional drill as a bypass water line to serve the houses and businesses along the route. This was the first directional drill water line project for the City of Greensboro.

Many benefits were gained from installing this service line during construction and for the long-term including:
  • Ability to avoid all utilities during drilling
  • Minimal interruption in service to homes and businesses
  • No temporary water line needed to serve customers during construction
  • All services moved out of pavement and heavy traffic.
With the new 4-in. service line in place, the replacement of the 1920s-era water line could begin. The project included replacing 3,000 ft of 12-in. cast iron pipe with 12-in. ductile iron pipe. As stated before, the initial estimate for dig and replacement of the water line was $1.3 million, with an estimated construction time of six months.

The equipment used for this larger project was a GrundoBurst 1250G, which provides more than 250,000 lbs of pull.

KRG Utility Construction crews worked 24 hours a day in 12-hour shifts from Friday evenings through Tuesday mornings to avoid heavy traffic congestion hours.

The project was divided into three sections with four main pits. Crews were able to safely barricade and plate the installation pits during off-construction hours between Tuesday morning and Friday evening. Because the 4-in. service line was installed, the 12-in. water line could be isolated and out of service for the duration of the construction.

For this application, TR Flex Ductile Iron pipe was used. This particular ductile iron pipe is ideal for trenchless technology because of its joint strength and the fact that no special pulling head is needed. The bell of the pipe fits into the pipe bursting machine’s expander head and is secured inside the bell by the pulling rod cone. The joints of the pipe are locked together by metal retainer clips, which lock the bell against the bead on the mate pipe.

All tees and crosses were excavated in order to cut all side connections to insure the intersected 6-in. lines were not damaged during construction.

After the pipe bursting was complete, the new pipe was cut and new tees and crosses were connected. Additionally, main line valves were installed throughout the project. Pressure testing and disinfection was completed as with standard water line construction.

The Wendover Avenue pipe bursting project proved that pipe bursting is not only a viable alternative for water line replacement for the City of Greensboro, it is highly beneficial:

  1. Traditional dig-and-replace construction was estimated to cost $1.3 million for the Wendover project. In reality, the pipe bursting project cost was $770,000, a savings of approximately $500,000.
  2. Traditional dig-and-replace construction had an estimated construction schedule of six months. The pipe bursting project was completed over three four-day weekends, working 24 hours each day in 12-hour shifts.
  3. Construction was completed without causing massive delays on Greensboro’s busiest thoroughfare and without a single public complaint.
  4. The use of fusible PVC and ductile iron for pipe bursting was highly effective.

Robbie Bald, P.E., is with the City of Greensboro, N.C., and Jeff Greene, P.E., is president of KRG Utility Inc., Lenoir, N.C.
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