Underwater Pipeline Construction Using the B.B.T

On February 24, 1987, the Greater Vancouver Sewerage and Drainage District awarded an $8.5 million contract to Dillingham-Manson. A Joint Venture for construction of the Iona Outfall-Submarine section. The work to be done under this contract involved the installation of approximately 10,500 ft. of twin 90 inch diameter steel outfall of which 1,640 ft.was twin 82 inch, 72 inch, and 64 inch diameter steel diffuser sections. The outfall extended from the end of the Iona Jetty into the Strait of Georgia near the mouth of the Fraser River. It was 350 ft. deep at the end of the diffusers. The tender documents suggested a method of installation such that the pipe was fabricated full length on the jetty complete with flotation pipe and pulled into the water. Dillingham-Manson submitted an alternative method with their tender and were the successful low bidder. The proposed installation method was to assemble the pipe into nominal 1,000 ft. lengths in Dillingham’s North Vancouver yard, launch them, tow them to the site, sink them and bolt together underwater. One of the most interesting aspects of the project was the development of a remote controlled underwater bolting tool (affectionately called the BBT). This tool brought the flanges of the pipe strings together, aligned them in 3 dimensions, rotated one flange to line up the bolts, stabbed the bolts and tightened them. After completing the operation, the tool released itself from the pipe. The tool was operated from the surface using hydraulic controls. It contained five wide angle, high resolution video cameras complete with special underwater lights so the operator could observe the operation. The tool was designed to be used without the aid of divers and is believed to be one of the most sophisticated ever developed. The paper will describe the development and operation of this tool. Dillingham Construction was awarded the Montgomery Medal for innovation in construction for this project.