Plymouth Road over Plymouth Creek: The Sinkhole that Stopped Traffic

摘要

The Plymouth Road bridge over Plymouth Creek in Montgomery County, Pennsylvania has always been plagued with sinkholes. In December 2014 a sinkhole surfaced adjacent to the downstream apron. By March of 2015 subsidence had migrated beneath the apron and east abutment and caused separation of the abutment from the superstructure and subsequently the bridge was closed on March 12th. Plymouth Road provides a vital link in the community due to its proximity to Interstates 276 and 476. The sudden closure required diversion of more than 15,500 motorists a day onto other heavily traveled roads in the region. Due to the extent of undermining and significant traffic impact of the closure, the Pennsylvania Department of Transportation decided to accelerate design and construction of the bridge replacement. A complete design package was delivered in a few short weeks and the project was moved to construction by April 27th. Construction was completed in August and included complete bridge replacement, a micropile foundation designed to withstand further sinkhole development beneath the bridge, repair of existing sinkholes, a concrete channel liner to control surface water, and grouting of the approach roadways and a portion of the downstream channel for stability in the karst terrain. Discussed in the paper are the history of sinkhole problems at the bridge, past remediation techniques, and the pertinent aspects of accelerated design and construction with a focus on the difficulties associated with karst terrain.