Case Study - MNRR Jump Span Temporary Support of Excavation for Proposed Foundation Installation-PPT Presentation

PPT Presentation

Pdf Summary

This case study describes the temporary support of excavation (SOE) and “jump span” system designed for replacement of the Metro-North Railroad bridge over Atlantic Street near Stamford Transportation Center.<br /><br />The existing 1896 bridge had limited roadway clearance and constrained traffic to one lane in each direction. The replacement project aimed to lower the roadway, widen the bridge, and build new foundations behind the existing abutments, approximately 16 feet below railway grade. Railroad service had to continue during construction, while major SOE and jump-span work was restricted to outages lasting only five to nine days. Additional constraints included overhead catenary equipment, limited headroom, and potential underground obstructions.<br /><br />The site consisted of granular soils over bedrock, with obstructions encountered during investigation and drilling. The design used drilled micropile soldier piles and welded bracing, allowing greater flexibility for field adjustments than the contract’s bolted-bracing concept. Design followed AREMA requirements and accounted for trains operating over the excavation-support system, including railway surcharge, train impact, braking and traction forces, and bridge axial loads.<br /><br />Construction was organized into carefully sequenced stages for SOE installation and excavation to fit within the limited outage windows and protect active railway operations.<br /><br />The presentation’s key lessons are that unusual site constraints demand tailored engineering, thorough planning, and precise staging; applying AREMA guidance can involve a learning curve; and safety must remain the priority when construction activities support multiple trains and an essential commuter corridor.

Keywords

support of excavation

jump span

Metro-North Railroad

bridge replacement

Stamford Transportation Center

micropile soldier piles

AREMA standards

railway construction

construction staging

temporary excavation support