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5 CHAPTER 2 Research Approach from (i) files owned by the research team, (ii) members of 2.1 Introduction ADSC: The International Association of Foundation Drilling, To achieve the objectives established for this project, the fol- (iii) other SNW contractors, (iv) DOTs, (v) research institu- lowing research approach and research tasks were established: tions, and (vi) published journals and reports. Chapter 3 pro- vides a description of the data and contains a discussion of • Review existing procedures for the design and construction data adequacy for calibration purposes. of SNWs according to the ASD and LRFD methodologies; • Compile load-test data from several sources; 2.4 Development of Resistance • Develop resistance factors through calibration of load-test Factors through Calibration data using appropriate reliability-based methods; of Load-Test Data • Compare designs of SNWs prepared with LRFD and ASD methods; and Resistance factors for the design of SNWs were developed • Prepare LRFD design and construction specifications for and calibrated applying reliability methods and using the val- SNWs to be considered by AASHTO for future editions of ues contained in the soil nail test database. The calibration the AASHTO LRFD Bridge Design Specifications. was conducted using the procedures presented in the publi- cation “Development of Geotechnical Resistance Factors and Each of these tasks is described in further detail in the fol- Downdrag Load Factors for LRFD Foundation Strength Limit lowing paragraphs. State Design” (Allen, 2005). Chapter 3 provides the results of 2.2 Review of Design and the calibration. Construction Procedures 2.5 Comparisons of Designs Based for Soil Nailing on the LRFD and ASD Methods First a review of the LRFD method as applied to geotechni- Calibrated resistance factors were used in LRFD-based cal applications and retaining structures was made. As part of designs of various SNWs. These designs were compared with this review, an evaluation was performed of LRFD methodolo- designs obtained using the ASD method for the same SNWs gies developed for other bridge substructure components that and load conditions. Differences of key design parameters in shared some common aspects with SNWs. Subsequently, a SNWs design were assessed and potential advantages of the review was conducted of existing procedures for the design and LRFD-based methodology were quantified. Proposed changes construction of SNWs focused on U.S. practice. Relevant state- to be considered in future editions of the LRFD Bridge Design of-the-art publications related to the design of SNWs, includ- Specifications were identified. ing Byrne et al. (1998), Lazarte et al. (2003), and other recent national and international references (e.g., Clouterre, 2000) 2.6 Proposed LRFD Design and addressing SNW design were reviewed. Construction Specifications 2.3 Compilation of Soil Nail LRFD-based specifications for the design and construction Load-Test Data of SNWs were developed as part of this research. Appendices A and B, respectively, contain the proposed design and construc- A database of soil nail load-test results was compiled to tion specifications, which are formatted according to the latest provide data for the calibration of resistance factors for soil nail pullout. Sources of information included load-test results LRFD Bridge Design Specifications (AASHTO, 2007).