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9 (upper wall) back wall sill geosynthetic load-bearing wall (lower wall) reinforcement modular block facing Figure 1-1. Typical GRS bridge abutment with a segmental concrete block facing. GRS abutments with a flexible facing have some distinct GRS abutments are generally much less expensive to advantages over the conventional reinforced concrete abut- construct than their conventional counterparts. ments. The advantages include the following: It has generally been assumed that the design methods GRS abutments are more flexible, hence more tolerant and construction guidelines of GRS retaining walls are to foundation settlement and to seismic loading. readily applicable to GRS bridge abutments. The approach When properly designed and constructed, GRS abut- has raised concerns as GRS abutments are generally sub- ments are remarkably stable. GRS abutments also have jected to a relatively high-intensity load that is fairly close higher ductility (i.e., are less likely to experience a sud- to the wall face. Basic design guidelines for Mechanically den catastrophic collapse) than conventional reinforced Stabilized Earth (MSE) bridge abutments have been pro- concrete abutments. vided by the National Highway Institute (NHI) reference When properly designed and constructed, GRS abut- manual, entitled Mechanically Stabilized Earth Walls and ments can alleviate the bridge "bumps" commonly Reinforced Soil Slopes Design and Construction Guide- occurring at the two ends of a bridge supported by con- lines, (Elias et al., 2001). The NHI manual also gives a ventional reinforced concrete abutments, especially design example for an abutment reinforced with steel strips. when they are on piles. Design and construction guidelines for GRS abutments GRS abutments do not require embedment into the with a flexible facing that are based on sound engineering foundation soil for stability. This advantage is espe- research are not available. cially important when an environmental problem, such as excavation into previously contaminated soil, is involved. RESEARCH OBJECTIVE The lateral earth pressure behind a GRS abutment wall is much smaller than that in a conventional reinforced The objective of this study was to develop rational design concrete abutment. and construction guidelines for GRS bridge abutments with Construction of GRS abutments is rapid and requires a flexible facing. The objective has been successfully only "ordinary" construction equipment. achieved.