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Replacing Water Mains Through The Middle Of The University Of Nebraska
Construction took an additional three months. Time was critical for this work as the improvements had to be completed prior to the beginning of a Special Olympics event.
Specifications required directional drilling at eight locations for segments in close proximity to critical surface features.
“However, either open-cut or HDD were allowed at other locations,” said McArthur. “The contractor elected to use directional drilling for the entire project, thus saving substantial restoration costs. HDD also was selected due to its limited impact on existing surface and landscaping features. HDD greatly reduced the concerns for excavations on campus and the potential for injury to students.”
All the new mains were 12-inch diameter restrained joint Certainteed Certa-Lok PVC pipe. The project contained three segments: one of more than 1,200 feet; 850 feet; and 800 feet.
There were twelve bores on the project with the longest at 600 feet and the shortest at 100 feet. Average depth of water mains was five feet but some areas were 15-feet deep to avoid underground steam tunnels.
“K2 Construction used a computer generated bore planner to show depths and distances of these facilities for planning the bores,” said McArthur. “This and careful monitoring of the drill tool location during the pilot hole helped ensure adequate distance between the new water main and the existing utilities throughout the project.”
Locations of existing utilities were visibly confirmed by potholing using a Tornado F3 Hydravac vacuum excavator. The same machine was used to keep the work site clear of drilling fluids.
Where excavations were required, steel plates were placed over the holes or the excavations were backfilled immediately after use.
For the bores, K2 used a Vermeer D36x50 HDD model. Powered by a 140-horsepower diesel engine, it develops 36,000 pounds of pullback, 5,000 foot pounds of rotary torque with a maximum spindle speed of 227 rpm.
Subsurface soils were primarily clay. Pilot bores were five inches in diameter backreamed to 16 inches. A Digitrak Eclipse with a 50-foot sonde transmitter tracked the path of the bore. A Vermeer Atlas Bore Planner was used to help plan the installation. All bores were made at times when campus activity was light.