After nearly four months of grueling work 50 ft beneath a state beach in Rhode Island, crews have finished drilling a 2,250-ft tunnel for the conduit that will carry power from the 30-MW Block Island wind farm to a National Grid switching station in Narragansett, R.I.

大卫·格雷夫斯（David Graves）是向罗德岛，纽约和马萨诸塞州的能源提供商讲话的人，他说，5月6日的完成将使公司在新泽西州的分包商LS Cable America在Deepwater Wind安装时开始安装Undersea Cable从五个离岸涡轮机到岛上电缆。他说：“我们的天气很糟糕，受到海洋的摆布，但我们准备于5月28日开始从大陆到岛上铺设20英里的电缆。”

格雷夫斯说，国家电网的传输工作部分成本为1.07亿美元，包括海底电缆以及大陆和街区岛上的变电站和交换站的安装和建造。

The wind farm—the nation’s first offshore demonstration project of its type—is now under construction at four port facilities, says Deepwater Wind. Steel jacket foundations are installed, and turbines are set for erection this summer, with grid connection by year’s end.

In addition to mainland work at Scarborough Beach, crews are drilling a 0.8- mile-long tunnel from Crescent Beach on the eastern side of Block Island to the new substation under construction, Graves says. “This is where our 20-mile cable, Deepwater Wind’s 8-mile cable and the Block Island Power Co.’s distribution system will all converge.”

Long Stretch

Drilling at Scarborough Beach began on Jan. 8 for the 24-in. high-density polyethylene conduit that will slide through and carry the undersea cable to a mainland parking lot, where it will be spliced to an underground cable that will run 3.5 miles to a switching station being built in Narragansett, Graves says.

Another 0.8-mile stretch of cable will run from the switching station to the existing Wakefield, R.I., substation, tying into National Grid’s distribution system. “It was daunting,” Graves says. “We went through multiple drill bits to get it done.”

Jim Yuille—vice president of horizontal directional drilling for Caldwell Marine International, another New Jersey-based project subcontractor—says, “The work is similar to sea drilling for power-cable installation that [the firm] has performed, but the rock at Scarborough Beach is some of the hardest ever.”

Optimizing

National Grid originally had planned to drill about 3,000 ft, from the Scarborough shore to the parking lot—where the manhole has been installed—but it opted to reduce the length to save on schedule. “The bedrock proved to be such a daunting exercise that we had to reconfigure our permits and cut about 750 feet from that drilling process,” Graves says.

Yuilles说，由12名工人组成的船员操作了钻井机器，驳船上另外18名支持该行动。在没有支撑的情况下，钻机钻9英寸。他解释说，驳船在钻头钻头上固定在钻头之前。

钻机在岸上然后附上铰刀widens the hole to 24 in. The on-shore drill rotates the reamer and supplies drilling mud to the hollow drill string. This process lubricates the hole and reamer while bringing back cuttings, which are separated from the mud in a shaker and pumped back into the drill for reuse. Each joint of the drill string is 30 ft long, “so they drill 30 feet, then add a section and drill another 30 feet and add another section,” Yuille notes. “The drill provides the rotation and the drilling mud. The barge offshore provides the force.”

According to Yuille, crews now are waiting for good weather to float into place the 2,200-ft-long conduit. “Once we complete the hole, we will pull the pipe conduit from offshore. The drill pulls the pipe conduit back through in one continuous pull,” he says. “The pipe is pulled by the drilling rig, and the barge has to work with divers to help guide it into the hole so we don’t overcome the pipe’s bending radius.”