GTR provided geotechnical and structural design of the temporary support of excavation for the support of lateral earth pressures, AREMA train loading, including braking and traction forces, and axial support of the Jump Span bridges for the staged construction of the new drilled micropile supported Abutments as part of the MetroNorth railroad bridge widened over Atlantic Street in Stamford, Connecticut. Originally constructed in 1896, the historic bridge consists of riveted steel thru-girders supported by unreinforced brownstone masonry abutments and steel pier bents which carried five (5) Metro-North Railroad (MNRR) tracks over Atlantic Street. The bridge structural components had deteriorated and it was classified as functionally obsolete due to the narrow underpass width as well as the existing minimum vertical clearance of 12’-4” which restricts the use of Atlantic Street by emergency service providers.
Unique design challenges included design and installation of pre-fabricated single track “jumpspan” bridge structures to limit rail service interruptions to individual 9 day track outages. Construction challenges included low headroom restrictions du to overhead catenary lines, and strict limitations on single track outages. To meet these challenges, GTR designed a temporary support of excavation system consisting of drilled soldier pile and lagging walls with tierods providing lateral support. The drilled soldier piles were installed using low headroom equipment along each phaseline between railroad ties. GTR’s SOE system was also designed to provide foundation support for the pre-fabricated jump spans. GTR’s SOE system permitted sequential demolition, excavation and construction during individual track outages such that live rail traffic was uninterrupted during each stage. Jump span design and construction facilitated drill micropile installation beneath live MNRR and AMTRAK traffic without interruption. GTR’s innovated jump span connection design resisted braking and traction forces through pre-fabricated top hats.
