AROUND MORETRENCH: Historic Pittsburgh, PA Bridge Re-build

April 6, 2015

As a full-service geotechnical contractor, Moretrench has the capability of providing turnkey solutions that address more than one construction challenge on a single site. This is highly advantageous to owners, general contractors and construction managers in terms of overall scheduling and streamlining the components of the project.  The wide range of tools at our disposal also allows us to respond rapidly with field-engineered solutions should an unanticipated subsurface issue arise during the course of the work.

Officially opened in October, 2014, the Butler Street Bridge replacement has been a long time coming.  The original reinforced concrete spandrel deck arch, completed in 1914, had deteriorated badly over the years, and the ravine it crossed had been filled to the underside of the span with incinerator ash.

Completed replacement structure

Caisson foundations were originally specified for the re-build, with Moretrench awarded the contract for the work.  However, caisson installation would involve excavation of 9,000 CY of ash, deemed landfill-sensitive,  as well as complete abutment removal. The general contractor, Trumbull Corporation, therefore sought an alternative  approach from its engineering consultant that would minimize excavation volume and abutment demolition.  This resulted in a micropile foundation system being accepted by PennDOT.  Since micropiles are also a Moretrench specialty, the transition to this method was accomplished seamlessly, with minimal delay.  Moretrench was also subsequently awarded the contract for beam-and-lagging support of excavation.

A primary challenge during production work was that 18 of the micropiles had to be drilled through up to 15 feet of the remaining heavily reinforced bridge arch structure as well as the abutment foundations.  With the installed locations critical to the overall design, Moretrench developed multiple alternative drilling approaches to ensure that deviation from the design location did not exceed the maximum six inches specified.  Crews worked around the clock in typical Pittsburgh winter weather conditions to successfully complete  the foundation work within the tight schedule.

See the full article from the February/March issue of Foundation Drilling magazine here.