Finite element modeling of micropiles and the influence of steel casing on load transfer mechanisms
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Micropiles made their debut as a cost effective way to retrofit existing historical structures. Recently, micropiles have increased in popularity all over the world and are being used for bridges, buildings, slope stability, antenna towers, and residential construction. Micropiles excel in difficult drilling conditions where other deep foundation methods are not plausible and consist of any combination of grout, rebar, hollow bar, steel pin, and steel casing. Due to their slender nature, defined less than 300 mm in diameter and lengths up to 100 feet, micropiles offer a distinct challenge in quantifying load transfer behaviors. Research at the University at Buffalo investigated the load transfer behavior of a single micropile and the influence of steel casing in soil using the finite element software ABAQUS. Soil models of sand, clay, and rock were fabricated. Simulated load testing determined micropile axial and lateral capacities for various cased length ratios, the cased length to micropile length, and were compared to field load tests. For both the clay and sand models an increase in cased length ratio resulted in lower axial capacities and higher lateral capacities. For the lateral case, diminishing returns on lateral capacities are observed for cased length ratios over 1:2. An increase in axial capacity was observed when casing to shale rock. The results are compared to various case studies, typical construction practices, and current design methodologies.