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Offshore Rescue

by Jonathan A. French, Associate; Camp Dresser & McKee, Cambridge, MA.,
Paul Gustafson, (M.ASCE), Associate; Camp Dresser & McKee, Cambridge, MA.,
John S. Murk, (M.ASCE), Manager; San Elijo Joint Powers Authority, Vice President, Camp Dresser & McKee, Cambridge, MA.,
Kellene M. Burn-Lucht, Assistant Manager; San Elijo Joint Powers Authority, Vice President, Camp Dresser & McKee, Cambridge, MA.,


Serial Information: Civil Engineering—ASCE, 1994, Vol. 64, Issue 10, Pg. 42-45


Document Type: Feature article

Abstract:

Restoration of wastewater ocean outfalls can be difficult, dangerous and environmentally challenging. Two recent projects, however, serve as examples of innovative outfall rehab. The first is the restoration of more than 500 ft of exposed outfall in San Elijo, Calif., which conveys treated effluent into the Pacific Ocean 8,000 ft offshore, at a depth of about 160 feet. Engineers developed a rehab solution known as the pile and cradle system that supported 16 ft sections of the outfall. Steel piles were driven on either side of the 35 pipe sections found to be at risk, and an adjustable steel collar was fastened to the pipe and piles to prevent pipe collapse caused by further sand migration, and to resist the force of currents and waves. The project team specified two basic construction techniques. In the near-shore zone, a cofferdam was built to protect the pipe and construction divers from the strong ocean current, and to control sand infiltration into excavations. For the deeper sections, a template frame straddled the pipe and guided the piles into position. To provide a stable above-water deck from which to conduct the piling and collar placement activities, a skid-mounted construction platform was pulled parallel to the pipe by a boat-mounted winch. The second project discussed is the 1 mi long Boca Raton (Fla.) outfall, which discharges to the Atlantic Ocean roughly 90 ft below the surface. There exposed segments were vulnerable to a Category 4 hurricane. As a result, armor block mats were placed in a 1,100 ft long reach to cover the exposed pipeline. The mats consist of thick, precast concrete rectangular armor units laced together by cables threaded through holes in the units.

Subject Headings: Pipe piles | Steel pipes | Steel piles | Ocean engineering | Cables | Project management | Sandy soils

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