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Suggested Citation:"Chapter 1 Introduction." National Academies of Sciences, Engineering, and Medicine. 2019. Proposed Refinements to Design Procedures for Geosynthetic Reinforced Soil (GRS) Structures in AASHTO LRFD Bridge Design Specifications. Washington, DC: The National Academies Press. doi: 10.17226/25416.
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9 Chapter 1 INTRODUCTION An important goal of this project is to produce recommendations for refinement of design procedures and specifications that can be integrated consistently into AASHTO LRFD Bridge Design Specifications (AASHTO 2017), specifically into Section 11.10 covering reinforced soil structures. Consequently, the qualitative and quantitative outcomes of this research, stemming from laboratory testing, numerical analysis, field tests, and reinterpretation of work conducted by others, is consolidated into recommendations for revisions of current design procedures that are compatible with AASHTO LRFD. That is, the approach followed herein involves modifying existing design procedures based on the findings of the multiple components of this research. The Research Team’s initial priority was to define the boundary for composite behavior of GMSE structures. Based on the findings from the experimental research component (NCHRP Project 24- 41, Final Report, Section 5), the proposed design procedure accounts for this boundary, while being fully consistent with AASHTO LRFD. The research results from the field monitoring program (NCHRP Project 24-41, Final Report, Section 6) and the numerical modeling study (NCHRP Project 24-41, Final Report, Section 7) were used to reassess current approaches, including correlations established by FHWA (2018) regarding the effect of vertical spacing. This information allows for rigorous integration of the findings of this project into the LRFD framework currently in AASHTO as proposed later in this section. Chapter 2 provides an overview of the current design procedures of geosynthetic-reinforced soil structures with closely-spaced reinforcement, highlighting the discrepancies between such procedures. With this background in mind, a total of five design aspects were identified to group the design recommendations stemming from the research findings. Accordingly, Chapter 3 provides the proposed revisions to current AASHTO design procedures that would allow incorporation of the effect of Sv into the design of geosynthetic-reinforced soil structures. Finally, Chapter 4 presents the basis to support the revisions proposed in the previous section, by referencing specific outcomes of this research.

Next: Chapter 2 Overview of Current Design Procedures for Geosynthetic-reinforced Soil Structures with Closely-spaced Reinforcement »
Proposed Refinements to Design Procedures for Geosynthetic Reinforced Soil (GRS) Structures in AASHTO LRFD Bridge Design Specifications Get This Book
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TRB’s National Cooperative Highway Research Program (NCHRP) Web-Only Document 260: Proposed Refinements to Design Procedures for Geosynthetic Reinforced Soil (GRS) Structures in AASHTO LRFD Bridge Design Specifications explores the effect of adopting a closely‐spaced reinforcement layout in geosynthetic‐reinforced soil structures.

While research since the early 1980s has identified the beneficial effect of closely‐spaced reinforcement in reinforced soil structures, such improvement in performance is not accounted for in the simplified methodologies established by the American Association of State Highway and Transportation Officials.

Considering the effect of closely‐spaced reinforcement may be particularly relevant in critical structures, such as load‐carrying geosynthetic‐reinforced MSE (GMSE) bridge abutments, which eliminate the use of deep foundations to support the bridge loads. In fact, the adoption of closely‐spaced reinforcement was identified as being particularly relevant for these type of structures, leading to specific design guidelines developed by FHWA for structures that became identified as Geosynthetic‐Reinforced Soil Integrated Bridge System, or GRS‐IBS.

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