Geotechnical & Structural Research

Challenge & Solution

The growing amount of waste tires collecting in landfills in Pennsylvania and the country represent both an environmental and an aesthetic concern.  At the same time, the transportation sector continues to struggle with the high cost of infrastructure improvement and upkeep in an era when public highway departments are faced with severe budgetary constraints.

Among these infrastructure expenditures are the significant costs associated with the construction of new and replacement bridge abutments and retaining walls.  The cost and design of these structures is impacted by the engineering properties of the backfill material used behind them.

This project for PennDOT’s Pollution Prevention- Strategic Recycling Program examined potential cost savings associated with the use of tire-derived aggregate (TDA) for backfill at bridge abutments and retaining walls.  Rhea is currently working as a subconsultant to Apex to complete this critical and timely project.

Project Description & Highlights

Rhea reviewed previous research findings from other states on the engineering properties and applications of TDA, and incorporated design guidelines and draft construction specifications developed by PennDOT for the use of TDA as structural backfill.  The current study evaluated various hypothetical combinations of structure type, structure height and foundation type for both TDA and conventional structure backfill arrangements.

Analyses were conducted using PennDOT’s Abutment and Retaining Wall Analysis and Design Computer Program, ABLRFD. Quantities and costs were developed and compared for all significant abutment and wall design components, including concrete, steel reinforcement, foundation piling, structure backfill, and geotextile.

Preliminary research findings indicate potential cost savings resulting from the use of TDA structure backfill.  The design savings appear to be generally more significant for taller structures and for structures with pile-supported foundations compared to spread foundations. In some cases, potential savings of approximately $500 per foot of structure have been identified. 


North Carolina