ABSTRACT
The Chesapeake Bay Bridge-Tunnel was created in the 1960s to build a fixed crossing at the entrance to Chesapeake Bay. Two immersed tunnels allow vehicular traffic to flow under the major shipping channels. To minimize vehicular traffic congestion, the Parallel Thimble Shoal Tunnel is being constructed.
The Parallel Thimble Shoal Tunnel Project is constructing a bored tunnel under the sea, between two existing artificial islands and in close proximity to an existing immersed tube tunnel already in operation.
The limited size of the existing islands required building new berms to allow the 13.25 m diameter earth pressure balance (EPB) tunnel boring machine (TBM) to be deployed from the artificial island to the offshore tunnel reach. This transition required innovative solutions to create a suitable environment to allow the TBM excavation. This paper describes the design development of this artificial berm in a sensitive environment, conceived to allow the EPB TBM excavation. A new concept was used for this purpose, placing oversized grout bags above the tunnel crown in combination with steel piles.
