A perfect storm of high winds, heavy, blowing snow and massive overflows from the Sagavanirktok (Sag) River wreaked havoc on the Dalton Highway and the trans-Alaska pipeline in spring of 2015.
The state-owned highway, which is the lifeline to the North Slope oil fields, was closed for days during March and was completely impassable April 6-12 as crews battled up to 18 inches of overflow caused by freeze-thaw conditions and natural ice damming on the Sag River.
This epic event left a huge mess – and exposed buried sections of the trans-Alaska pipeline to the open air and moving water. While the pipeline’s integrity was never in danger, the situation called for an immediate response, with Ahtna Construction handling some of the most difficult work for Alyeska Pipeline Service Co., the pipeline operator.
The pipeline is buried five-feet deep along this section and the flooding exposed it in six locations.
The repair was complicated, as Alyeska Project Manager Shaune O’Neil explained. “You can’t just throw gravel on top of the pipeline. We had to do a careful assessment, checking to make sure the pipe coating and the pipe weren’t damaged, along with the pipeline’s cathodic protection.”
That meant excavating around the pipeline. “We had to go two feet below the pipeline and build side slope and, since the pipeline was buried at five feet below the surface at these points, it meant we had to excavate a trench to the 11-foot level before the pipe inspections could be done.”
Ahtna mobilized Aug. 29 and finished its work in early December. In total, Alyeska and its four contractors expended 48,000 man-hours of work, moved about 50,000 cubic yards of gravel, 10,000 cubic yards of large rock and 350 cubic yards of sand.
“Our crew performed extremely well in the harsh, winter conditions,” Scott McIlroy, senior program manager at Ahtna Construction, said. Alyeska called on Ahtna Construction on short notice, but its team was eager to help. Fourteen Ahtna Construction team members were sent to help expose what damage had been done and to help prevent future damages from occurring. “The work environment was a little rough,” McIlroy said, “but that’s what we do.”