FEATURE ARTICLE SPECIAL ISSUE : The History of Micropile Technology Installing micropiles beneath the historic ferry building on Ellis Island Micropiles are small-diameter foundation elements constructed using specialty drilling and grouting methods. Micropiles have evolved since their introduction into the North American market in the 1970s from being lightly-loaded (less than 30 kips) elements used primarily for remedial applications to today’s high-capacity, often hybridized foundation systems, for both remedial and new-bui ld projects. Micropiles now occupy a substantial market segment in North America. Dr. Fernando Lizzi from Fondedile, S.A. invented and patented the pali radice (root piles) technique in the 1950s as an innovative solution to structural damage in war-torn Europe. Many structural underpinning and historic retrofit projects were completed successfully throughout the continent. Fondedile entered the U.S. market in 1970, and structural under- pinning projects incorporating micropiles were conducted in the U.S. and Canada in the early 1970s. But progress was slow, and Fondedile eventually left North America in 1990. The use of small-diameter structural elements was regarded as innovative but unproven in many segments of the U.S. engineering community. Demonstration AUTHORS projects were completed in 1977, including the slope stabilization in Mendocino, Calif., and the Foothills Parkway in North Carolina where micro caissons were used, but growth of the market remained limited. Growth of a Technology In the 1980s and early 1990s, U.S.-based specialty contractors seasoned in the installation of rock and earth anchors — work that often combines injection of Date Project 1977 Mendocino Forest Service Road, CA 1977 California tests, CA 1980 Orange County Prison, NY 1984 Armstrong County, PA 1987 Coney Island, NY 1988 I-78 Bridge over Delaware River, PA/NJ 1989 Pokomoke River Bridge, MD 1990 Bernstein Building, Baltimore, MD 1993 United Grain Terminal, WA 1994 San Dimas Channel Bridge, CA 1999 Exton Mall expansion, PA Table 1: Early evolution of pile projects Allen Cadden, P.E., D.GE, Schnabel Engineering, Inc.; Jim Bruce, P.Eng., Geo-Foundations Contractors, Inc.; Mary Ellen Bruce Large, P.E., D.GE, Deep Foundations Institute; and Peggy Hagerty Duffy, P.E., D.GE, ADSC: International Association of Foundation Drilling DEEP FOUNDATIONS • MAY/JUNE 2016 • 97 First high-capacity prestressed micropiles in soil, 50 ton. (tested to 200 ton) Soil piles, 70 ton tested to 250 tons Very high capacity, structural failure in load test Seismic retrofit, load test to 640 kips 160 ton piles in karst completed while mall remained in operation unsanded grouts and small-diameter drilling using limited-access drilling equipment — began to solve challenges using the same equipment and methods while adopting the concepts of early micropiles. Table 1 contains a list of landmark U.S. micropile projects, and Table 2 lists mega projects that further influenced the growth of the technology. Contractors continued the push for acceptance despite the lack of published guidance. Significance Demonstration of reticulated micropiles for slope stabilization Comparison of remedial pile technologies First cased micropile, post tensioned, 20 ton First A-Wall slope stabilization 15-30 ton, low headroom 100 ton pile in karst
