Birmingham Bridge Emergency Repairs: Micropile Foundation Retrofit

When two spans of the Birmingham Bridge, a vital link in the Pittsburgh area transportation system, dropped up to 200 mm (8 in.) overnight, rapid response and a team approach was key to minimizing the impact to traffic and to the subsequent remediation. Initial inspection, initiated within hours of the discovery, revealed that the steel rocker bearings at Pier 10S had over-rotated and failed, causing the girders to drop onto the pier cap and resulting in damage to the pier itself. Repairing the bridge and reopening the roadway to traffic as soon as possible was critical. A closely-coordinated effort between PennDOT and all members of the quickly-assembled bridge retrofit team was instrumental in ensuring the immediate temporary stabilization of the structure to allow traffic flow to resume during the subsequent bridge rehabilitation. The cause of failure was determined to be the "ratcheting" of debris-choked and corroded rocker bearings at the top of the pier. However, this paper discusses the complete evaluation of the structure, conducted concurrent with emergency temporary shoring measures, including analysis of the original foundation system, and design, installation and testing of new micropile foundation systems that replaced the inadequate deep foundations at both Pier 10S and Pier 10N.