In 1968 Dominion Energy Virginia erected a series of 18 towers across the James River to carry two transmission lines from south of the river to points in Newport News. The company built the tower foundations with marine-grade, corrosion-resistant steel that was billed to last for decades. By the 1990s, however, it was evident that the steel foundations were eroding. If they deteriorated sufficiently, one of the towers would collapse, putting the Virginia Peninsula at risk of disruption to its electric service.
The utility encapsulated the steel “H pile” foundations with a fiberglass jacket under the waterline and with a putty-like compound above in the hope of preventing further corrosion. The fix didn’t work. A 2013 inspection revealed rust still eating away at the foundation.
“While the 2013 inspection revealed we had a corrosion problem, further investigation found that we had a bigger problem than we thought,” says Mark Allen, Dominion’s director of transmission construction. There was no way of knowing precisely when, he says, but “eventually the towers would have collapsed.”
One remedy would be to build parallel towers and power lines, but that option would cost $50 million. It would be far preferable to repair the foundations in place. But Dominion could not take a chance of knocking the transmission line out of commission by cutting out the bad steel beneath the water and replacing it with good. In 2013, Dominion was under orders to close the two main coal-fired boilers at its Yorktown plant and was struggling to gain regulatory permission to build a new transmission line upriver near Jamestown. There were only two sets of transmission lines serving the Virginia Peninsula, so taking down the Surry-Winchester and Chuckatuck-Newport News lines would have left the entire region vulnerable to blackouts.
Dominion’s engineering staff came up with a solution that wound up costing rate payers only $25 million. The story was chronicled by local media but never given attention elsewhere in the state. When the project garnered recognition by the Southeastern Electric Exchange earlier this year, Bacon’s Rebellion thought it worth re-telling as an example of the trials and tribulations of maintaining an electric transmission grid.
No one had tackled a job like this before. The foundations of the 18 towers varied in depth between four feet near the riverbanks to 40 feet near the navigation channel, and the company had to cap the foundations to about 15 feet above the waterline, says Allen. The company also had to maneuver around restrictions on time and location due to protections for osprey and cormorant nests on multiple towers, a peregrine falcon nest on the nearby James River Bridge, and fish migrations from Feb. 15 to June 30, not to mention weather conditions.
Divers entered the water, which was so dark at times that they couldn’t see their hands in front of their faces, to install clips on the side of each H pile. To these clips they fastened rebar cages. Around the rebar cages, the construction contractor put in an epoxy-fiberglass jacket to facilitate the pouring of a “cementitous grout” that would become the new foundations for the towers. The design, which fully shielded the old “H-pile” foundations from the concrete caps above water to four feet below the water line, eliminated the need to cut out existing steel below the water surface.
“We were able to use what was there,” says Allen, who commends the creativity of the engineering team. “Instead of an H pile supporting the tower, we have a rebar cage and concrete encapsulation.”
The retrofit, which was completed in 2015, should last another 40 years.There are currently no comments highlighted.