GRS-IBS Reinforcement Spacing-ERS

Boundary Conditions for Composite Behavior of Geosynthetically Reinforced Structures (GRS)

Geosynthetic mechanically stabilized earth (GMSE) systems have been widely used in U.S. to construct earth retaining structures, access ramps, and bridge abutments since 1970s. Recently, Federal Highway Administration (FHWA) has been implementing an alternative system for bridge abutments called geosynthetic reinforced soil – integrated bridge system (GRS-IBS) that can withstand significantly higher loads than GMSE and yet still be constructed faster than the conventional concrete abutment systems and can tolerate differential settlements. The primary difference between the GMSE and GRS systems lies within the vertical spacing of the reinforcements. The typical spacing between the reinforcements in GRS-IBS is 8 inches whereas in GMSE the spacing can be much larger (up to 32-inches or more).  

The vertical reinforcement spacing has a significant influence on deformation properties of the structures when subjected to loadings and hence it is a criterion to create a boundary between the structures. A closely-spaced structure creates a composite behavior, which is different than the behavior observed when reinforcements are placed far apart from each other replicating a similar behavior as tie-backs.

This research mainly focuses on identifying criteria to define the effects of closely-spaced reinforcement in GRS-IBS (with geotextile reinforcement) in order to define the boundaries for a composite material and to use the findings of this study to provide support to develop design parameters that may be incorporated in AASHTO LRFD Bridge Design Specifications.

This research involves data collection from a full-scale GRS-IBS abutment by Virginia Department of Transportation located in Virginia's Staunton district. The research involves in developing a rigorous instrumentation program to be incorporated into the construction and monitoring the behavior of the structures during and after construction. The instrumentation program includes instruments such as string thermistor, water content reflectometer (WCR), wire line extensometer, soil extensometer, strain gauges, and survey targets. The relevant data to be collected are related to stress conditions behind the facing of the structure, vertical and horizontal deformations in different sections of the structure, stress conditions within the soil mass and changes within the observed behavior during and after construction. Field data will be collected for about two years to monitor changes. The collected data will be correlated with results from small-scale laboratory tests and the findings from laboratory and field studies will be used to develop numerical analysis that will be used to define the criteria for closely-spaced geosynthetically reinforced structures.