Dewatering effects on structures adjacent to central artery/tunnel project

Groundwater control during cut-and-cover tunnel construction of a half-mile segment of the Central Artery I-93 Northbound Tunnel requiring excavation to more than 100 feet below ground surface resulted in temporary depression of the groundwater and settlements to adjacent structures, including two high-rise buildings. The reduction in groundwater levels outside the excavation limits generally had a greater effect on adjacent structures than any other construction activity, with the amount of settlement varying with distance from excavation, subsurface conditions and foundation type. Generally uniform settlements were recorded within the footprint of the high-rise building discussed herein, with maximum settlements reaching approximately (1)/(2) inch. This paper describes the dewatering along a portion of the Central Artery Corridor, measures used to minimize groundwater lowering outside the excavation limits, and effect on three adjacent structures. Comparisons between predicted versus measured performance are presented, including time history plots of piezometric levels and settlement at each building.