No Gamble Here: HDD a Success in Atlantic City
April 19, 2012Installed more than a century ago, the two 36-in. diameter cast iron sewerage force mains transporting all of the sanitary waste out of Atlantic City, N.J., were deteriorating and becoming a problem for their owner, Atlantic City Sewerage Company (ACSCo) to maintain.
Much of the ACSCo’s infrastructure had been replaced over the last several years. However, sections of the New York and St. James force mains — as commonly called by the ACSCo — crossed waterways and marsh lands in Atlantic City. Recognizing that replacing these force mains in environmentally sensitive areas would require a trenchless technology, the ACSCo retained the engineering services of Buchart-Horn to develop a plan and prepare the construction documents.
After a prequalification and competitive bidding process, Carson & Roberts Site Construction and Engineering Inc., a nationally recognized civil contractor, was awarded the contract to horizontally directionally drill (HDD) approximately 2,200 lf, for two new 42-in. HDPE force mains.
In addition to the two large horizontal directional drills, the project’s scope of work also included more than 2,500 lf of 42-in. HPDE DR 17 to be installed via open-cut, 200 lf of exposed 36-in. DIP, which needed to be supported on pile caps, and the removal of portions of the existing force main.
In March 2011, Carson & Roberts kicked off the project. First up, the contractor needed to figure out how to stabilize the tidally influenced ground to support the drill equipment. After consulting with a geotechnical engineer, a design consisting of wick drains, geotextile fabrics, aggregate and matting was developed and installed. Carson & Roberts also needed to raise the entire work area by approximately 3 ft to prevent any possible flood damage to our equipment should a Nor’easter storm occur.
Next, Carson & Roberts mobilized its 1 million-lb DD 1100 American Augers drill rig to the jobsite. The most challenging aspect of this HDD was not encroaching on a property corner directly in-line of the ideal drill path. To avoid having the new force mains on someone else’s property, a path and profile was designed with an 800-ft compound radius. With Horizontal Technologies Inc. of Texas providing its steering services, the pilot hole never deviated more than 2 ft from the intended plan.
After almost knocking the stake over on the exit side, crews proceeded to pull a 36-in. reamer down hole, followed by a 60-in. ream pass. After a few passes with a 48-in. ball, the entire 2,200 lf of 42-in. OD HDPE was pulled into the hole in just under a 12-hour period. The same process was repeated for the second drill and it was completed within a three-week period.
Horizontal directionally drilling a 2,200-lf shot of 42-in. HDPE pipe is not uncommon these days; however, accomplishing it with a more than 72-degree horizontal bend in it and repeating it within 25 ft of the first drill made it the most complex drill Carson & Roberts has completed to date.
“Pushing the envelope for drilling was an understatement,” according to one of Carson & Roberts’ most experienced drill superintendents. “The most I ever bent a drill steel was 60 degrees. At 72 degrees, we were all walking on eggshells until we saw the pipe come out of the hole. And having to do it all over again is truly a remarkable feat.”
“Such an extreme horizontal radius would not have been possible without suitable ground conditions,” stated Scott Murray, P.E., senior vice president for Carson & Roberts trenchless division. “At 50 ft deep, the organic over burden of the marsh land and channel quickly turned into a cohansey sand layer that provided enough stability to steer the pilot. However, we did install a 12-in. conductor barrel through the organic layer to serve as bearing support for the drill steel.
“Fortunately, we had enough room to fuse and stage the entire 2,200 lf of product pipe on rollers prior to pullback. With the pipe filled with water, the pullback force never exceeded 150,000 lbs.”
By July 2011, the HDD portion of the project was complete and Carson & Roberts had successfully installed two parallel 42-in. HDPE DR 11 force mains over 2,200 lf each.
While the open-cut installation and pile cap work continued, Carson & Roberts project managers meet with the ACSCo personnel and the design engineer, Dennis Tracey of Buchart Horn, to review the tie-in procedures for activating the newly installed force mains. Since shutting down the existing sanitary force mains that transported all of the waste from Atlantic City was clearly not an option, a well thought out construction sequence that included a temporary bypass line was agreed upon and put into action.
With the balance of the open-cut and aerial piping finished as scheduled, the first new force main was placed in service late September 2012 followed by the second less than a month later – well within the mandated deadline for the project.
Jill Bullock is with Carson & Roberts, Site Construction and Engineering Inc. To view a video on this project, visit Carson & Roberts’ website at www.carsonroberts.com.
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