Dry Cut-and-Cover Station for MBTA in Boston

With the recent opening of the Silverline Phase II the MBTA did not only put in service a 2 mile long section of running tunnels containing technically challenging segments such as immersed tubes through the Fort Point Channel and NATM binocular tunnels at the historic Russia Wharf Building, but also opened two new underground stations along the alignment.

Courthouse Station, a slurry wall supported cut-and-cover station was successfully waterproofed with a flexible membrane waterproofing system protecting the architectural interior, its support elements and installations such as conduits and wires from corrosion. The waterproofing system consists of an invert and roof waterproofing terminated at the slurry walls and wall waterproofing applied to the exposed slurry walls and protected by CMU walls.   The wall waterproofing is interrupted where the roof and invert slab connect to the slurry walls, as well as at the mezzanine slab connection to the slurry walls.  There the water is collected with horizontal drain pipes, discharged to the invert level and through lateral drains in the invert slab to the main track drains. The roof waterproofing includes a sectioning system, which in the case of a breach in the membrane allows local repair through preinstalled repair and grouting pipes.  This approach greatly reduces repair cost caused by loss of grout.

The cut-and-cover tunnels west of the station and the cut-and-cover tunnels of the adjacent World Trade Center Station are waterproofed with a fully circumferential flexible membrane waterproofing, while the cut-and-cover tunnels east of Courthouse Station leading up to the immersed tube tunnels feature a roof and invert waterproofing with exposed slurry walls. 

Based on the superior results over the years, DSC promotes the use of flexible membrane waterproofing systems, which are common in mined underground structures, in cut-and-cover applications.   Besides at the Silverline in Boston, MA, this type of waterproofing was used by WMATA in Washington, D.C., and the Port Authority in Pittsburgh, PA, to protect their underground cut-and-cover stations and tunnels.