Micropiles: the state of practice. Part II: design of single micropiles and groups and networks of micropiles

Abstract

This series of papers summarizes the research project initiated in 1993 by the US Federal Highway Administration to review the state of practice, case studies and design methods of micropile group systems. Following a brief description of the recently adopted classification system for micropile design previously outlined by Bruce et al. (1997) (part 1), this paper (part 2) presents a summary of recommendations for the design of single micropiles and groups and networks of micropiles for selected engineering applications, including direct structural support and in situ soil reinforcement. Preliminary estimates of the ultimate axial and lateral capacity of micropiles, as outlined by different authors, are presented first. Design guidelines which have been developed generally through observations on full-scale testing and field experiences are discussed with regard to cohesionless soils, cohesive soils and rocks. Group and network effects are investigated and preliminary conclusions are presented along with proposed design guidelines for micropile groups. Existing analytical approaches are evaluated through comparisons with experimental data obtained by different investigators on the engineering behaviour of micropile groups and reticulated micropile networks under different loading conditions.