871/872 & 879/880 Transmission Rebuild

2021

This project consisted of rebuilding two different double circuit lines in Northern NY for Iberdrola USA (Avangrid). The 871/872 segment was a two phase line rebuild spanning 10 miles. The rebuild started at Kent Falls Substation and ran to High Falls Substation. The 879/880 segment was a 7 phase rebuild spanning 18.5 miles. The rebuild ran from Hammond Lane to Rainbow Falls Substation.

Challenges:

Wet and Sandy Ground Conditions

Certain areas of the project had ground conditions with a high sand and silt content. This required flooding concrete caissons to maintain positive head pressure to stabilize each hole. Additionally, permanent casings were used for some shafts due to depth and diameter with drilling depths as deep as fifty feet. A vibratory hammer was used to install permanent casings to stabilize those shafts to ensure stable shafts.

Extremely Hard Bedrock

Bedrock encountered in certain portions of the project was sandstone with quartz that had a comprehensive PSI greater than 30,000. The bedrock was extremely hard and abrasive and conventional rock drill tooling was only yielding 3 inches per day. In order to stay on schedule down the hole hammers were utilized. Six and seven foot full face down the hole hammers were utilized requiring five 1600 CFM air compressors running at full capacity to drill the rock.

Geographical Location/Schedule

The project spanned from Ausable Chasm NY to Saranac NY and required working through multiple winters in Northern NY. January of 2019 had a two week stretch where crews worked through temperatures that saw a real-feel high of 5 degrees and a low of -26 degrees. Equipment had to be run around the clock to prevent freezing and drilling underwater required drill tooling to be constantly thawed with heaters. Crews worked through this stretch with zero incidents and stayed on schedule.