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2015FallShotcreteEMag

Goin’ Underground Northern Boulevard Crossing Tunnel CQ039 By Frank Townsend Tgram linking Long Island Rail Road trains the tunnel alignment, extending to bedrock forContaminated plumes in the area also dictatedthe installation of a protective frozen arch above-he Northern Boulevard Crossing tunnel isa crucial link for the East Side Access Pro to Grand Central Station, New York City. It is a complete groundwater cutoff. The freezing of the 125 ft (38 m) long sequentially excavated (SEM) ground costs the New York Metropolitan Trans- tunnel. The tunnel is situated approximately 55 ft portation Authority (MTA) $11,000 per day. (17 m) below the groundwater table and was Every day the liner completion could be acceler- mined through glacial deposits. The tunnel align- ated, the more savings to the MTA. A value- ment also crossed beneath a pile-supported, engineered approach was given to the MTA to elevated railway line; a six-lane street; and an shotcrete this liner in lieu of traditional cast-in- active below-grade subway structure (refer to place. This offered both savings in time and Fig. 1 and 2). construction cost. Without the shotcrete alter- native approach, an elaborate, costly, and time- consuming tunnel form system would have to be engineered, delivered, and assembled in the tunnel for traditional formed cast-in-place concrete. The contractor estimates that close to 2 months were saved using the shotcrete alternative. Superior Gunite’s scope was to expeditiously shoot the structural liner of this tunnel to then allow quickly unfreezing the ground and trans- fer the load from the aboveground structures. Coordination with the contractor allowed Super- ior Gunite crews to use the same scaffolding system used by the lathers installing the reinfor- cing bars, again saving time and money (refer to Fig. 3 and 4). Fig. 1: East Side Access overall project scope Challenges Preparation of a plan and logistics were critical to the success of the project. Through a very tight relationship with our concrete supplier, Ferrara, we mapped out trucking delivery routes to miti- gate the New York City traffic to avoid lost time and waiting times on trucks. Ferrara had a Quality Control representative on site to work through any possible quality control and address issues on the spot, which fortunately were minimal. Due to the site constraints, laydown area was limited. We installed our primary and backup pumps inline so if we had mechanical issues we could easily swap the line and deal with the pump Fig. 2: CQ39 Excavation on the off-shift. This system proved important, as 52 Shotcrete • Fall 2015


2015FallShotcreteEMag
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