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Job Complications Lead To AXIS System Solution
It took the AXIS system less than four hours to bore the 160 feet into the existing manhole. Once completed, the drill head and casing were pulled back into the entry pit and the head was uncoupled from the carriage assembly.
To install new pipe, the AXIS system typically uses one of two methods. For rigid pipes, after the drill head reaches the exit pit, sections of new pipe are substituted for drill casing, and the carriage assembly thrusts forward, jacking the pipe through the bore hole.
If job site conditions permit, it may be possible to pull pipe back through the bore hole. For this procedure, after the drill head reaches the exit pit, it is removed and replaced with a pulling head, which attaches to the product pipe, and it is pulled back through the bore hole. With the pullback method, it is possible to attach a reamer to the puller head to increase the diameter of the hole in order to install pipe that is larger than the pilot bore.
Because of site conditions in Kannapolis, Mann said a decision was made to push the new ductile iron pipe through the bole hole from the entry pit with an excavator using a nose cone and push cap to push the new pipe through one joint at a time. Grout was installed around the pipe through a tremmie line.
With new pipe in the ground, the launch pit was filled in and the street surface repaved. It took only two days from the time the launch pit was excavated until the project was completed.
The project was the first experience with the AXIS system method of installation for both Hendrick Construction and the city of Kannapolis.
"The method served the specific requirements of the job very well," said the city's Bissinger.
Vermeer's Milligan said he believes that as more projects are completed and more people are exposed to the new technology, it will become an option on an increasing number of projects.
"The AXIS system provides several benefits that are not found in other trenchless installation methods," Milligan emphasized. "Some methods can achieve accurate bores with less than a one to two percent grade, but they are time consuming. Other procedures can compete with open cut for speed of installation, but lack the ability to hold the tight grade tolerances mandated for gravity sewers. The AXIS system combines speed and accuracy into the same package, while adding the benefit of an environmentally friendly, non disruptive, trenchless installation."