Automated Monitoring System used to Support Drydock Operations at Electric Boat

The Electric Boat facility in Groton, Connecticut consists of three Graving Docks, each supported by interlocking circular and diaphragm cofferdam structures. Owned and operated by the General Dynamic's subsidiary Electric Boat Corporation, these graving docks are used for the construction and maintenance of the United States Navy's submarine fleet. Graving Docks 1 and 2 were constructed between 1961 and 1968, followed by Graving Dock 3, known as the Land Level Construction Facility, which was constructed from 1975 to 1977. In May 2004, sheetpile cofferdam cell S-2 at Graving Dock 3 experienced an interlock failure during a routine dewatering evolution performed to drydock the USS Jimmy Carter. This event rendered Dock 3 unavailable for submarine construction and launched a series of initiatives at the facility to investigate the cofferdam failure, stabilize and repair cell S-2, and monitor and evaluate the condition of all three Graving Docks. As routine submarine maintenance continued at Graving Docks 1 & 2, geotechnical instrumentation played a pivotal role in restoring confidence in the ability of the aging cofferdam structures to support the construction and maintenance of nuclear powered submarines. A total of ninety-four (94) vibrating wire piezometers were installed near the base of each cofferdam cell to monitor hydrostatic levels. These instruments were automated using a customized data acquisition system (ADAS) to provide real-time changes of in-situ pore pressures. This data is used during routine but critical dewatering activities to monitor hoop stress conditions in each cofferdam cell and provide the basis for controlling the rate of flooding and dewatering at the Facility. This automated system has demonstrated that pore pressures can be controlled within individual cells to remain within operating range and therefore restore confidence in the Facility so that time sensitive construction and maintenance activities can continue.