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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).
