BACKGROUND: Micropile foundations consist of small-diameter (typically less than 12 inches) drilled and grouted non-displacement, reinforced elements. Such foundations can be constructed in situations of low-headroom, restricted-access, obstructions, and vibration-sensitive sites. However, current micropile foundation design does not incorporate rational reliability-based geotechnical resistance factors, and many state departments of transportation do not have sufficient data or resources to do such calibrations. There was a need to identify the parameters that influence the resistance factors for micropile foundations and develop reliability-based geotechnical resistance factors and specifications that can be used for various design and construction methods. These factors and accompanying specifications should provide an increased level of confidence in the design and help highway agencies in making decisions regarding the use of micropile foundations.
OBJECTIVE: The objective of this research was to develop reliability-based geotechnical resistance factors for axially-loaded micropiles and related specifications.
STATUS: Research is complete. The research (a) identified geotechnical resistance factors for axially-loaded micropiles and (b) recommended specifications and commentary for consideration by AASHTO. Published as NCHRP Reserch Report 989.
