Pivotal moment for cable reburial project

Thu, 01/14/2021 - 5:45pm

For many months now, crews contracted by Orsted and National Grid have been busy working on the reburial of a portion of their two undersea electric transmission cables, one that goes out to the wind farm, and one that connects Block Island to the mainland. The cables were not originally installed at the desired depth of six feet, and had become exposed in areas due to shifting sands.

While workers were visible constructing a 3,500-foot conduit that stretched the entire length of Crescent Beach from Baby Beach to Scotch Beach, what else they were doing has been somewhat of a mystery.

Islanders and visitors have witnessed two liftboats, the M/V Ram XV and the M/V Ram Vll, off the shore of Fred Benson Town Beach and other support vessels in Old Harbor, as well as tons of equipment, supplies, and trailers in the parking lot of the beach.

It turns out that crews from JT Cleary have been busy drilling a tunnel under the sea floor from just north of the Beach Pavilion, under the dunes, and out to a pit near the liftboats. Using a process known as horizontal drilling, workers drilled the tunnel, expanding it with reamers to the desired circumference. The tunnel in places is 30 to 40 feet under the ocean floor. Town Facilities Manager Sam Bird told The Block Island Times that geologically speaking, the drill was cutting through glacial till, which includes large rocks, rubble, and seams of clay and sand.

On Thursday, Jan. 7, crews floated and towed the conduit from the beach out beyond the liftboat and then pulled it back to shore through the tunnel. The operation, which started at 8 a.m. was slated to take 16 hours, and went off without a hitch, although it had been delayed a couple of days for “adverse sea conditions.”

This phase of the project, the pullback of the conduit, was a complex operation involving several assist boats, dozens of workers and several machines on the beach. To start, the head of the conduit was lifted and floated into the water at a slight angle to the beach. It was attached to a tow line connected to the Berto Miller and ever-so-slowly tugged out to sea.

Meanwhile, workers, placed all along the length of the pipe, gently lifted it and inched the conduit along the beach towards the water, trying not to bend it. As they did, one of the support vessels got between the conduit and the beach to help guide it out.

Now that the first conduit has been installed, workers will start the process all over again – this time for the National Grid cable, which will require a somewhat shorter tunnel. Once the cables have been drawn through the conduits, they will be spliced onto the existing cables in the pit offshore. During that process, which will take place later this spring, power from the cable will be shut down and the Block Island Power Company will revert to its diesel generators to supply the island with electricity.

A microwave tower is being installed to supply broadband during the time of the outage.