Thermal Grout, HDD Make 6,200-Foot Electrical Transmission Installation Possible

By Jeff Griffin, Senior Editor | December 2012, Vol. 67 No. 12

Waldemar S. Nelson & Company was the lead project consultant responsible for handling the detailed engineering and design, material procurement and construction management. The prime contractor was Southeast Directional Drilling. M&M Pipeline Services/Energy Services South was subcontractor for site preparation, handling and welding 36-inch steel casing and site restoration.

The Constellation Group was the thermal grout consultant. Geotherm USA performed thermal testing.

For the bay crossing, Southeast Directional Drilling (SEDD) mobilized two HDD rig spreads. Both drill rigs were modified American Augers machines with pullback capacities exceeding 500,000 pounds, said Mel Olson, vice president of SEDD. Each rig spread included mud systems, mud pumps, drill pipe tooling, and other support equipment.

Further, the bay crossing was not a typical HDD installation.

“We installed approximately 220 feet of 60-inch conductor casing under the Florida Avenue substation at the south end of the crossing to protect the active substation from impacts of the HDD process,” said Olson. “The conductor barrel casing installed by pneumatic hammer was sized so that its 220-foot length would extend through the limits of the substation and its 60-inch diameter size would allow the largest downhole tool -- a 48 inch reamer -- to pass through. The conductor casing remained in place after completion of the HDD segment.”

After driving the casing to the desired length of approximately 220 feet, it was augered out with 42-inch diameter auger segments connected directly to the rig’s drill stem. Once the final soil material was removed from the conductor casing, a 16-inch diameter centralizer pipe was installed to center the drill stem while completing the pilot hole and ream passes.

Simultaneous drill

After the conductor casing was installed, the substation would not need to be de-energized for the duration of the directional drilling, including the installation of the 36-inch steel casing and HDPE conduit bundle installation.

“The two drilling rigs began drilling simultaneously from opposite ends of the long crossing until they reached the point of intersection near the center approximately 3,100 feet away from each rig,” explained Olson. “Next, the secondary rig retracted drill pipe while the primary rig’s drill pipe followed it up the borehole without deviation from the planned path. During this phase, special tracking software is required in conjunction with the hole intersect method.”