GTR provided geotechnical and structural design, real-time instrumentation and technical support for the historic East Avenue Bridge in Norwalk, Connecticut to facilitate the installation of upgraded utilities beneath the active railroad bridge abutments, in advance of bridge replacement. Built in 1905, the historic bridge was constructed of unreinforced brownstone masonry abutments which are susceptible to settlement and cracking due to construction vibrations. Unique design challenges included designing a modular and adjustable strut and wale braced temporary earth support system that could be fabricated, installed and relocated under low headroom conditions while being robust enough to withstand lateral pressures from the unreinforced brownstone bridge abutments with uninterrupted Metro-North and AMTRAK rail traffic overhead. The existing bridge spans approximately 20 feet of roadway and is classified as functionally obsolete due to the narrow underpass width and vertical clearance of just 12 feet. The AUP project required excavation depths of 20 feet below the bottom of existing bridge abutments thereby encroaching on zone of influence of both abutment foundations.
To overcome these challenges, GTR worked closely with the Owner and the CMGC to develop a special earth retaining system that met the stringent site-specific vertical and lateral deformation tolerances. GTR evaluated global stability and designed an internally braced drilled soldier pile and lagging system reinforced with inner steel pipe to resist the anticipated lateral, seismic, braking and traction forces. GTR’s custom adjustable hydraulic strut system was employed to increase lateral resistance at the abutment footing locations. GTR installed and monitored Automated In-Place Inclinometers, Deformation Monitoring Points and Bi-Axial Tiltmeters to ensure structure stability throughout each stage of work. GTR’s design was successfully implemented to facilitate installation of the upgraded utilities
