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TECHNOLOGY Micropiles for Structural Support

Abstract This technical paper discusses the Micropiles brief history, Micropiles Classification, Drilling Techniques, Grouting, Reinforcement, Design Concept, Testing procedures and Guidelines of Micropiles. The paper provides a simplified step-by-step design approach. These include geotechnical strength limit states, other structural considerations, service limit states, corrosion protection and Micropiles testing procedures. Keywords : Micropiles Classification, Drilling Techniques, Grouting, Reinforcement, Design Concept Introduction Micropiles are small diameter piles (less than 300 mm) can be installed in almost any type of ground where piles are required with design load (3 Tons to 500 Tons). The first use of micropiles dates back to the early 1950’s in Italy, where new methods of underpinning for existing structures were needed to restore structures and monuments damaged during World War II (Lizzi, 1982). Dr. Fernando Lizzi is commonly recognized as the inventor of micropiles in the form of the root or palo-radice. Dr. Lizzi was a civil engineer and Technical Director with the Italian specialty foundation contractor Fondedile and obtained the first patents for root piles in Italy in 1952. This early form of micropile technology was used extensively in Europe for the restoration of various structures and monuments. Fondedile introduced micropiles into North America in 1973 by performing a number of projects, mainly in the Northeastern United States. By the mid 1970’s a number of US specialty foundation contractors previously engaged in drilled and grouted anchor work had developed their own variants of the technology. There was slow growth of the technology in the time period between the mid 1970’s and the mid 1980’s with Fondedile closing their North American venture for economic reasons. (Bruce and Juran, 1997) There has been a rapid growth in the specification and use of micropiles in the United States since the mid 1980’s to early 1990’s partly as a result of FHWA research efforts, trade association promotion efforts and the development of various publications offering standardized design and specification guidelines. In the early 1990’s, the Intermodal Surface Transportation Efficiency Act (ISTEA) provided massive funding for the rehabilitation of highway infrastructure in the United States. As part of this effort, the FHWA undertook a number of research and development projects associated with specialty geotechnical construction to encourage innovation in geotechnical applications and produced several design manuals including the first on micropiles. This was the beginning of the surge in micropile use in the United State. In 2006 and 2007 respectively, the International Building Code and the AASHTO LRFD Bridge Design Specifications incorporated design code sections for micropiles thus making way for further expansion of applications in both building and highway construction. Micropiles currently are widely specified and used in all construction sectors worldwide.