The Massachusetts Bay Transportation Authority (MBTA) is addressing accessibility throughout their facilities. Improvements at the Commuter Rail Station in Salem, Massachusetts include a five-level parking garage replacing the existing parking lot, a pedestrian bridge replacing the existing stairway connecting track level with downtown Salem, two accessible elevators, and a full-length accessible high-level platform. Subsurface explorations at the site encountered fill overlying loose, potentially liquefiable saturated sands, overlying soft marine clay deposits extending to till and rock at about 60 to 80 feet depth. Deep foundations bearing on rock were recommended for structural support of the garage, bridge, and platform. Ground improvement using vibratory stone columns (VSCs) was also recommended to address the liquefaction and lateral spreading potential, and to improve the seismic site classification from Class F to Site Class E. The project team evaluated value-engineering options. The final design included the installation of over 470 Controlled Modulus Columns? below the garage and bridge footings. Over 825 VSCs up to 30 feet in depth were installed below the parking garage and platform. Post-VSC treatment testing was conducted during construction to review compliance with the specified performance criteria. The cooperative design and installation required coordination between the design and construction teams to maximize cost and schedule efficiency for the project. These methods allowed the project to move forward, ultimately saving the client millions of dollars in construction costs.
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