This report presents the findings of research undertaken to develop a rational design method and construction guidelines for using geosynthetic-reinforced soil (GRS) systems in bridge abutments. This report will be of immediate interest to professionals responsible for designing and constructing GRS structures. The use of geosynthetic-reinforced soil (GRS) systems as the foundation for or as integral structural components of bridge abutments and piers is receiving increased http://onlinepubs.trb.org/Onlinepubs/nchrp/nchrp_rpt_556.pdfattention and interest. The soil mass of GRS systems is reinforced in layers with a polymeric geosynthetic (e.g., geogrids or geotextiles), and the layered reinforcement is attached to facing elements that constitute the outer wall. Because the facing elements are commonly composed of articulated units that are not rigidly attached to each other, the wall is deemed flexible. Various materials, including natural rock, concrete block, gabion, or timber, may be used for the flexible facing. GRS structures are more forgiving to differential foundation settlement thus minimizing the bump that commonly This report may be accessed by Internet users at develops between the roadway and bridge. GRS structures are more adaptable to lowquality backfill, easier to construct, and more economical than their conventional counterparts. GRS structures can be put into service quickly, can be built by maintenance personnel, and are especially well suited to projects constructed in areas that are difficult to access with heavy equipment. GRS structures are an economical alternative for temporary structures, because of their easy demolition and the recyclable nature of their components, and for emergency work, because of reduced lead time and lower equipment requirements. Full-scale tests conducted by the FHWA and by the Colorado DOT on GRS bridge abutments and piers with segmental modular block facing have demonstrated excellent performance characteristics and very high load-carrying capacity. Even with the significant advantages of GRS systems, the use of GRS structures in routine highway bridge construction has not been widely adopted. The primary obstacles to adoption of GRS systems in bridge construction are threefold. The first obstacle is the lack of a rational and reliable design method for such bridge-supporting structures. For example, although the vertical spacing of the reinforcement has been found to affect the performance of the structure, current design methods fail to reflect this important fact. Also, field-measured strains are known to be drastically smaller than those predicted by current design methods. Clearly, the current design methods are not sufficient. The second obstacle is the lack of well-developed guidelines and specifications for constructing the structures. Such guidelines and specifications are critical to the successful application of this technology. The third obstacle is the perception that polymeric geosynthetics may not be strong enough to meet the high service loads expected during the design life of large bridge structures. Under NCHRP Project 12-59, “Design and Construction of Segmental Geosynthetic- Reinforced Soil (GRS) Bridge Abutments for Bridge Support,” the University of Colorado at Denver developed a rational design method and construction guidelines for GRS bridge abutments and approaches with flexible facing elements. After an extensive literature review, the researchers conducted full-scale experiments and a thorough analytical study. Based on the research results, a rational design method and construction guidelines were developed and design examples illustrating the design computation procedure were conducted and documented. NCHRP Report 556 consists of the project final report and two appendixes. A third appendix, “Verification of DYNA3D/LS-DYNA” is not included in this report, but is available as NCHRP Web-Only Document 81 and can be found at http://www4.trb.org/trb/crp.nsf. (Author/publisher)
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