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Construction Update:South & Division Cross Dikes Stage 1

Project Photos

Project Description

The first construction job for the Craney Island Eastward Expansion was awarded to Great Lakes Dredge & Dock Co. (GLDD) in September 2010. Stage 1 of the South & Division Cross Dikes is in progress, with GLDD building the initial sand lifts required to construct the dikes and installing Prefabricated Wick Drains (PVDs) to strengten and consolidate the sand.

The sand for the dikes is brought to Craney Island by the Liberty Island hopper dredge, which can carry more than 5,000 cubic yards of material at a time. Constructing the dikes will require it to dredge approximately 1.2 million cubic yards of sand from the Atlantic Ocean Channel (AOC) and transport it to the project site.

GLDD has designed and constructed a unique piece of equipment specialized for this project, called a spill barge. The spill barge, which is connected to the Liberty Island by a pipe, works like a sprinkler to disperse the pumped sand along the alignment of the proposed dikes. The spill barge allows even layers of sand to be placed. After placing the sand via spill barge, the contractor will install wick drains, which allow the soft subsurface clays to consolidate and strengthen.

The contract also includes demolishing a section of the existing rock jetty that forms the northern boundary of the Craney Island rehandling basin. This demolition is necessary to allow for future access channels to Craney Island Marine Terminal.

Current Status

Dredging/Sand Placement: Great Lakes Dredge and Dock Company (GLDD) finished placing the first set of sand lifts along the footprints of the South and Divison cross dikes in late February. They continue work on installing a drainage system of wick drains in the division dike that will significantly speed up the process of consolidating and strengthening the soft clay foundation that lies beneath the dike footprints.

To install the PVDs, the contractors designed and constructed a modified barge built specifically for the Craney Island project. The barge was modified by installing pipes into the deck to match the spacing specified for the PVDs. This set-up allowed the contractor to limit the number of times the barge was repositioned in order to optimize production of the project.

Demolition of East End of Craney Jetty: GLDD subcontractor WF Magann demolished the outer 300 feet of the Craney Island rock jetty, removing a total of 11,169 tons of debris.

Building the south and division cross dikes - shown in the rendering above - is the first step to create the Craney Island Eastward Expansion.

Schedule

Phase	Date
Contract Awarded	September 2010
Notice to Proceed	November 2010
Final Completion	September 2011

Dredging/Sand Placement

	PVD installation continues along the north side of the South Dike.
	Great Lakes Dredge & Docks specially-designed spill barge distributes layers of sand onto the footprints of the south and division cross dikes.
	An aerial shot of the project location shows the existing Craney Island in the background and the location of the eastward expansion in the foreground. The expansion will add 522 acres to the east side of Craney Island.
	This aerial view of the project site shows the contaiment cells of Craney Island. The cells are constantly filled with dredged material and then drained of excess water, as evidenced by the pool of water within the island.
	The Liberty Island hopper dredge is assisted by several tugboats while taking its position in the harbor to transfer sand to the spill barge.
	Tugboats position the pipe for the next load of sand.
	This view from on the spill barge shows a load of sand being dispensed into the footprint of the cross dikes.
	The Liberty Island dredge is 315 feet long.

	The Liberty Island dredge is a hopper dredge. Hopper dredges are designed to vacuum material from the sea floor through drag arms that load the material into the hold of the vessel.
	The LIberty Island holds sand dredged from the Atlantic Ocean Channel until it is ready to be placed into the dike footprint.