The project removed approximately 5,000 cu yd of contaminated sediments adjacent to the Norfolk combined sewer overflow outfall on the Duwamish River. The location, trapped between two low level fixed bridges, required installation of a temporary trestle to mobilize a 125-ton crawler crane onto a special barge with containment cells and anchor winches. All materials were mechanically dredged according to a detailed contour plan requiring 2-4 ft cuts.
The first phase consisted of the construction of a habitat area by building an underwater rock berm from elevation -50 ft MMLW to elevation -20 ft MMLW. The area behind the berm was backfilled with 84,000 cu yd of dredge spoils. The second phase required the dredging of 392,000 cu yd of material and placement of riprap slope protection. There were 43,000 cu yd of unsuitable material that was excavated and disposed of at a designated landfill.
The project began with the relocation of approximately 1,000 sq ft of eelgrass. Then a 250ft long by 50 ft wide trench was dug. Serving as a foundation for the diffuser, three, 4 ft by 12 ft articulated concrete ballast mats were placed at in 55 ft of water in Puget Sound. The 620 ft. long, 54 inch HDPE outfall pipe was sealed at each end and pulled from the beach into the water. While it was floating, 23 concrete weights were attached. Each weight was over 15,000 pounds. After attaching the onshore end to its tie-in point, we used controlled submergence to sink the pipe into the trench and onto the mats. Finally the trench was backfilled and the beach was restored to its previous appearance.
This project was an environmental cleanup of a Superfund site. Dredging and sediment dewatering were carefully planned and executed to avoid spreading contamination during the work. Additionally, the project included demolition of 105,000 sq ft of pier decking and removal of 2,600 timber piles. 90,000-tons of slope rock and under pier capping sand were installed. The Association of General Contractors of Washington honored this project with the 2006 Construction Excellence Grand Award.
The Yaquina North Jetty project required rebuilding the jetty with previously placed rock that storms and natural wave action had displaced over the years. Typically, more rock is added at the tip to replace rock that has washed out. However, over the years so much rock had been added that it encroached on the entrance channel. A 165-ton derrick barge removed the displaced rock at the tip of the jetty using a large rock grapple. The salvaged rock was then placed onto a 1,200-ton capacity flat deck barge and transferred to the north side of the jetty. In order to take advantage of the short summer season, the rock removal operation went on around-the-clock, seven days a week. 43,000-tons of rock were removed and relocated, with the largest pieces between 20 to 32-tons each.
General Constructions work started almost 2 miles offshore where an outfall tunnel is connected to the seabed by a 9 ft. diameter riser structure. The 10 ft. diameter seabed outfall trunk line originates at the riser and proceeds west for 4,500 ft., to a 320-ton wye structure. From the wye structure, two diffuser lines extend 2,000 ft. to the north and south along the seabed. This project required dredging 210,000 cubic yards of excavation, and placement of 350,000 tons of rock to bed, ballast and armor the 1.6 miles of outfall pipe. All work was performed 2 to 4 miles offshore, and at an average depth of 100 ft.
This project included the demolition of select sections of an existing wharf including asphalt pavement, precast concrete deck panels, cast-in-place concrete pile caps, removal of precast, pre-stressed concrete piling (14 in. square and 16 in. octagonal), and removal of a concrete bulkhead supported on sheetpile. The demolished wharf sections were replaced with similar segments constructed with 24 in. octagonal piling. A new concrete bulkhead was constructed on the existing sheetpile. Other activities included removal and reinstallation of the 130-ton transfer spans (ramps) and installation of a new transfer span (furnished by the owner). The work was completed in two phases to accommodate terminal operations. Other work included upgrading the water system and providing new electrical service to the re-constructed wharf sections.
General Construction was a subcontractor to Tucci & Sons for this project that included the construction of a 250 lin ft concrete wharf at the Port of Tacoma. The wharf was founded on 24 in. pre-cast octagonal piles. Work included installation of steel sheet piling and steel batter piles for the bulkhead and installation of a fendering system. The fender system at another berth was also upgraded prior to a critical fish closure. This work occurred in an active shipping channel.
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