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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 Teamâs 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.
