ANCHORAGE (AP) An offshore drilling derrick in Knik Arm near downtown Anchorage is not seeking oil.
The rig is taking soil samples for a $1.25 million seismic study that will determine the best way to expand the Port of Anchorage dock.
The derrick is a self-contained combination drilling rig and barge fitted with long support legs that can be raised or lowered independently. The city-owned port, as part of a broader $227 million redevelopment project, plans to expand the dock 400 feet seaward, adding 83 acres to the existing 100.
Port officials are considering two basic dock designs.
The first, developed by engineering firm Peratrovich, Nottingham and Drage, is called ''open-cell sheet pile.'' That approach uses U-shaped, sheet metal cells to create membranes, sort of like a honeycomb, that are filled with gravel, forming the base on which the dock rests.
The alternative is a traditional dock supported by piles driven deep into the sea floor. Engineering firm Tryck Nyman Hayes has submitted a design proposal that would use that method.
Port officials have been leaning toward the open-cell sheet pile design, but a city-funded study last summer found that the soil on the ocean floor might not be strong enough to support that kind of dock.
The jack-up drill, owned and operated by Signal Hill, Calif.-based Gregg Drilling & Testing, began working last week and so far has drilled three holes and taken soil samples from as deep as 250 feet, said Kevin Bruce of the port staff.
Over the next month and a half, 40 to 50 samples will be taken. Gregg is sending samples to Terracon Consulting, which will analyze them and prepare a geotechnical report that will serve as a guideline for the dock-expansion design.
The port is paying Gregg $1 million for the drilling and sample collection work. Terracon is getting $250,000.
The expansion, financed through federal grants, state grants, port profits and revenue bonds, also includes plans for building cruise ship, barge and ferry terminals, improving rail access, and deepening the harbor from 35 feet at low tide to 45 feet to accommodate larger ships.
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