The Chesapeake Bay Bridge-Tunnel’s Parallel Thimble Shoal Tunnel Project reached a milestone in February 2023 as Chessie began her initial excavation of the new tunnel. However, after advancing approximately 700 feet from the launch pit, Chessie encountered an unknown obstacle under the Bay bottom. Pieces of steel were found on the conveyor belt of the TBM that were soon identified as parts of an old anchor, manufactured by W. L. Byers & Co.
While it is not an uncommon occurrence to encounter obstructions while tunneling, this “find” of a large anchor in the path of the TBM suspended tunneling.
From June 2023 to early December 2023, CTJV developed a plan that included the construction of a safe haven into which the TBM could be driven to allow for a maintenance intervention. This plan involved performing ground improvements of the soil in and around the cutterhead. These improvements were completed by injecting foam grout to seal the area around the cutterhead and between the cutterhead and the safe haven located in front of the TBM. This was all done to prevent any potential cave-ins, or blow-outs, at the cutterhead. By grouting the ground in front of the TBM, CTJV was able to pressurize the excavation chamber and prevent water and sand from flowing into the excavation chamber.
Bulkheads at the front of the TBM, with air-lock chambers, allowed workers to gain access to the cutterhead for inspection, remove any remaining anchor debris and replace any damaged tools. All of this work was completed underground, under the seabed, in front of the TBM.
Upon removal of the anchor pieces, CTJV then performed a full inspection of the cutterhead. It was determined that 389 of the 442 tools on the cutterhead required replacement. Each of these tools weighs approximately 150 pounds.
A total of 48 wear plates were also replaced.
A full inspection was also performed on the mechanical and drive systems to verify that no further damage was done to the tunnel boring machine.
INSPECT…GRIND…WELD…
Pictured above are workers as they inspect the tools of the cutterhead; grind the tools of the cutterhead; and weld the tools and wear plates of the cutterhead.
On April 8, 2024, CTJV began tunneling once again. As of late April, CTJV is averaging a progression of 50+ feet each day and has completed more than 600 feet since resuming tunneling, with a total of more than 1,400 feet of tunnel liner installed, or approximately 25%, since tunneling began in February 2023.
The anchor obstruction resulted in the addition of 241 days to the scheduled completion of this project.
While tunneling progress may have been delayed, work continued on Two Island as CTJV prepares the island to receive Chessie. Much progress has been made and the receiving pit was completed in late 2023.
Pictured above is #2 island Open Approach, looking south.
On the south end of the island, the marine crews continue with the construction of the engineered berm. This engineered berm will be a newly constructed piece of the island that will allow Chessie to transition from the Bay bottom to #2 island, as she prepares to break through.
Once mining is complete, CTJV will begin to construct the roadway, install the tunnel’s electrical/mechanical systems and construct the support buildings. Current forecast for completion is late summer 2027.
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