Coal, Gas, Renewables

Cianbro Using Cableway in Penstock Replacement

Issue 10 and Volume 103.

Cianbro Corp. has been awarded a $5.5 million contract to complete a Niagara Mohawk Power Co. project. Cianbro will replace a penstock that is 12.5 feet in diameter. The pipe takes water from a canal off the Hoosic River and carries it 1,200 feet across a ravine to a surge tank, where the water is sent through four, six-foot penstock sections to hydroelectric turbines.

“What makes this job unique is the 100-foot deep ravine,” said David Nardon, Cianbro’s regional manager. “It creates a tough access to the series of pedestals and abutments that support the penstock on both sides of the ravine.”

Crane access would be difficult because of the extreme pitch on both sides of the ravine, leading Cianbro to choose a construction tactic used successfully on the Hoover Dam. Cianbro will use a cableway that is a series of twin 2-inch diameter steel cables spanning the ravine to support an unmanned trolley with two, 10-ton electric power hoists. “A cableway is what they used to build the Hoover Dam, due to its access characteristics,” Nardon said. “It’s perfect for this application because we’ll be able to lift sections of the old pipes out and lower sections of the new pipe in without having to build access roads on the slopes to bring in cranes.

“It would have been a nightmare to build access roads to get close enough to the penstock to use cranes. They have a restricted capacity in both reach and height, and must be level to operate safely. The slope would have been difficult and costly to make level enough for the cranes.” Cianbro was the only bidder to propose the cableway solution.

The project is expected to take about five months. Temporary walkways will be constructed for riggers and welders will work inside and outside the pipe.