This report contains proposed specifications for the design and construction of soil-nailed retaining structures. Despite their advantages in cut applications, these structures are not available to some state DOTs, due to the lack of guidance for their use in AASHTO’s standard specifications based on load and resistance factor design (LRFD). This report will be of interest to geotechnical engineers and construction managers, who would like to promote a more common utilization of soil nailing. The soil-nailing method of earth retention is the preferred retaining wall option for many cut applications, because their advantages may include cost, speed of construction, construction flexibility, and aesthetics. Federal Highway Administration (FHWA) Demonstration Project No. 103 developed comprehensive design and construction manuals for temporary and permanent soil-nailed structures. These FHWA soil-nailing manuals contained a detailed design protocol for allowable stress design (ASD) and a preliminary load and resistance factor design (LRFD) approach. The AASHTO Standard Bridge Specifications, the AASHTO LRFD Bridge Design Specifications, and the AASHTO LRFD Bridge Construction Specifications do not include guidance for soil-nailed structures. In the absence of AASHTO LRFD specifications, some state departments of transportation will not use soil-nailed retaining structures. Given the advantages of soil-nailed structures, there is a need to develop proposed standard design and construction specifications for soil-nailed structures for incorporation into the AASHTO LRFD Bridge Design and Construction Specifications. The objective of NCHRP Project 24-21 was to develop these proposed LRFD design and construction specifications for soil-nailed retaining structures. To accomplish the project objective, the research agency, Geosyntec Consultants, used the existing FHWA guidelines on soil nailing, conducted a comprehensive review of current soil-nailing design and construction guidance for both ASD and LRFD specifications, and drafted proposed LRFD design and construction specifications. The research team subsequently identified, evaluated, and calibrated a range of resistance factors, based on the level of detail and confidence in the accuracy of the site investigations for multiple soil nail wall (SNW) project scenarios. These resistance factors were used with current AASHTO load factors to design SNWs using LRFD methodology and compared to SNWs designed using ASD methodology for the same project scenarios to demonstrate equivalence. (Author/publisher)
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