Slurry Trench Wall Replaces Structure Underpinning

Construction of the Charles Center Station of the Baltimore Metro required a cut-and-cover excavation 66 feet (20 m) deep in a major street in the central business district of Baltimore, Maryland. Several high-rise buildings were so close to the excavation that it was necessary to remove portions of the spread footing foundations which extended into the proposed station excavation. The contract documents required that the spread footings adjacent to the excavation be underpinned using steel pipe piles jacked to end bearing on bedrock. When it was apparent that difficulties in installation would result in substantial delays in project completion, the piles were deleted and a redesigned concrete slurry trench wall was constructed to confine the soil beneath the adjacent building foundations. Instrumentation data and visual observations indicated that the concrete slurry trench wall was successful in controlling settlement of the adjacent buildings to acceptable limits