Massachusetts Route 7A in Lenox, Massachusetts; the route’s Sheffield section was rebuilt over the Housatonic Railroad in 2014 | Wikimedia Commons
The $1.1 million bridge cost 49% less than the estimated price of the original conventional design, according to the Federal Highway Administration . The project also had to accommodate a railway crossing that required a 105-foot-wide bridge with a 30-degree skew. FHWA reported that the $1.1 million GRS-IBS bridge represented a 49% saving in comparison with the estimated cost of the original conventional design. In June 2014, MassDOT and FHWA held a workshop in Massachusetts that was focused on GRS-IBS. Its construction changed the structure supporting conventional bridge components, and the cost comparison of a $1.1 million project coming in 49% below the estimated conventional design was the clearest result.
The Route 7A bridge therefore served two purposes: replacing an aging railway crossing and giving Massachusetts engineers a full-scale example of how reinforced soil could be used for a skewed bridge over an active rail line. The system changed how the bridge approaches and abutments were constructed, and FHWA describes GRS-IBS as a method that combines reinforced soil with the bridge superstructure rather than treating the roadway and bridge as entirely separate conventional components. The Route 7A project in Sheffield was presented as the state’s first example, while two additional Massachusetts projects were already being developed.
The Route 7A project presented a more demanding application, since the bridge had to cross an active railroad and was built with a 30-degree skew. FHWA later identified it as one of the larger GRS-IBS structures that was constructed at the time, with abutments roughly 24 and 28 feet high. FHWA reported that the 2014 project was built with minimal disruption to train traffic, and the completed structure provided the wider roadway and pedestrian facilities that were required for the replacement while using the reinforced-soil system underneath.
Because the abutments use readily available fill material and reinforcement instead of some of the heavier conventional concrete construction, fHWA says the technology can reduce construction costs. The geosynthetic reinforced soil portion uses alternating layers of compacted granular fill and sheets of geosynthetic reinforcement. The integrated bridge system places a bridge superstructure directly on those reinforced soil abutments, which creates a continuous transition between the road and the bridge. FHWA had been promoting GRS-IBS through its Every Day Counts program in order to build smaller bridges more quickly and at lower cost.
