Gas To The Ozarks

By Jeff Griffin, Senior Editor | May 2013, Vol. 68 No. 5

“Ninety percent was open-cut with pipe buried to depths providing four-feet of cover above the pipe,” Brown said. “The other 10 percent was installed by horizontal directional drilling, primarily road and river crossings and the three long lake bores. For excavation, two 440-horsepower, 150,000-pound Tesmec M5 trenchers were used.

Along the route of the transmission line will be seven regulation stations to regulate the pressure of the natural gas as it passes from the steel line into the distribution lines.

Essential bores

Critical elements of the six-inch transmission line are three bores under the lake, all in the last 10 miles of the steel transmission line.

The water crossings were at three primary bridges: a 3,400-foot long bore at Niangua Bridge; 5,800 feet under Hurricane Deck Bridge; and a crossing of 3,700 feet at Community Bridge. Depth of the lake bores will average 80-feet through rocky conditions.

“The most difficult parts of the project are installing the steel pipe through the extreme hills and under the lake,” said Brown. “Soil data gathered during construction of the bridges helped designers plan for conditions the bores would have to pass through.”

J.F. Construction Services, DeWitt, MO, subcontracted the lake crossings. A one-million-pound pullback Vermeer D1000x900 HDD unit will make each bore. An 11¼ -inch bit provides a pilot hole large enough to install pipe without backreaming. Plans call for all bores to be surface launched, exiting on the opposite side of the lake.

For each installation the six-inch steel pipe was welded into a single string along the road. Space is tight, but crews must work with the area available, Brown said.

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The 3,400-foot Niangua Bridge crossing was made first. “There were no surprises or complications that the crews were not able to deal with,” said Brown. “With the Niangua bridge bore complete, crews moved to the toll bridge for the second lake bore.”