The substantial upsize wasn’t the only issue at hand. The existing 18 inch reinforced concrete pipe was as close as two feet from some of the largest Progress Energy overhead distribution power poles, which help provide power to most of northern Atlanta. In addition, a network of fiber-optic lines that supplies communications services to more than half of downtown Atlanta was buried in close proximity to the pipe. To make the project more challenging, also close by were an environmentally sensitive creek, a wildlife preserve, and an elite parochial school.

Atlanta city officials realised that replacing this line was going to be no easy task, as every contractor that they approached turned the project down due to the level of difficulty.

The surrounding utility infrastructure mandated that a trenchless solution would be necessary to replace the 1,000 ft section of pipe. These obstacles, plus the close proximity of a creek and the position of the existing pipe under the edge of a road, made pipe bursting the most practical trenchless method.

Pipe bursting involves driving a powerful bursting head through an existing utility pipe, fracturing or cutting it in the process, then pulling in new pipe of equal or greater size. Pipe bursting is efficient because it follows the path of existing utilities, reduces utility strike risks, and eliminates up to 85 per cent of excavation work compared to open-cut methods.

Because the project involved a quintuple upsize, it was classified by the International Pipe Bursting Association (IPBA) as a Class C or ‘experimental’ burst. A standard upsize is 2 inches; expanding the pipe diameter 10 inches, from 18 to 28, amounts to a quintuple. With so many challenges in addition to the upsize, experimental was definitely an appropriate term for the project. Impossible was the term most contractors gave it when asked to submit a bid!

Brent Scarbrough & Company (BS&C) of Fayetteville, Georgia, was willing to take on the challenge. In fact, BS&C was the only contractor in the area that demonstrated the confidence and capability to get the job done, thus earning the contract from the City of Atlanta. In business since 1985, BS&C is one of the leading site development companies in the south east United States, providing a wide range of services including erosion control, clearing and grading, and installation of sanitary sewers, storm drains, water lines and hardscapes.

The success of the project would require extensive planning and collaboration among the contractor, utility owner and equipment manufacturer. One of BS&C’s first steps was to contact HammerHead Trenchless Equipment to discuss details of the replacement. A HammerHead technician was sent to assess the specifics of the job.

Project Manager for BS&C’s pipe bursting division Jon Murray said “We had numerous conversations about the equipment and bursting tools. The proper equipment is always the key to a successful burst. By using HammerHead we were confident that the equipment would perform and help us complete our jobs with great success.”

The most immediate concern was the quintuple upsize, which involved a substantial expansion not only for the pipe burst but also the burst head, which had an outside diameter of 33.4 inches. Walking the path of the job, the technician noticed the sections of pipe that had been exposed by erosion.

This prompted concern that the lack of density of the ground in these exposed areas could cause the hammer to come out of the existing pipe. To prevent this, HammerHead would have to design and build a special bladed pilot that would keep the burst head and the hammer inside the existing pipe.

“The staff at HammerHead provided excellent technical support and immediate response to mechanical needs,” said Mr Murray.

Another major issue was the power distribution poles running parallel to the existing sewer line. The poles were made of solid concrete, 90 to 100 ft tall, and anchored 20 to 30 ft below ground. Representatives of Atlanta Power & Light would be a constant presence on the jobsite to ensure that the poles were not dislodged or moved.

And then there were the fiber-optic communication lines that connected half of northern Atlanta’s phone and internet service. In many areas these lines were right on top of the sewer line, so fiber contractors were given time to place temporary lines next to the power lines in order to maintain service throughout the project.

Also taken into account was traffic flow in the area. In planning the job, BS&C contractors and a HammerHead representative took extra time to walk the job and observe traffic flows to determine how to minimise project downtime, as the Department of Transportation would only allow BS&C to work on the road until 5 pm.

“As a team, Scarbrough and HammerHead devised a plan that helped overcome the large upsize of the sewer line, the close proximity of the power poles, and the traffic control plan,” said Mr Murray.

Equipment selected for the project included HammerHead 24 inch pneumatic pipe bursting hammers, a HammerHead HydroGuide HG20 winch, and the customised burst head and pilots.

In February 2010, after extensive planning and preparation, it was finally time to begin the replacement process. For the first burst, BS&C was able to complete a 400 ft section in about three and a half hours. The next burst was longer, 550 ft, but it only took a little more than four hours.

Throughout the pipe bursting process, power and communications services were maintained, traffic flowed without significant delays, school remained in session, and the surrounding environment was not affected. Thanks to careful planning, the collaboration of many dedicated professionals, and state-of-the-art HammerHead equipment, the City of Atlanta now has a new sewer line that can meet its demands.

In Atlanta, Georgia, HammerHead and Brent Scarbrough & Company teamed up to complete a tricky sewer upsize project, using pipe bursting.