Micropiles are deep foundations that are 12 inches or less in diameter although typically they have a diameter between 3 to 10 inches. They are typically constructed with steel casing and/or threaded bar and high-strength cement grout. Micropiles are most commonly made up of high strength steel casing and rebar, but can also be installed in some conditions with hollow-bar systems, which are stabilized with pressure grouting in lieu of casing. Capacities vary depending on the micropile size and subsurface profile. Installation can be achieved by rotary drilling, augering, driven or vibrating tooling. Micropiles are particularly efficient where natural or man-made obstructions occur, in limited access or low-headroom conditions and in karst geology where rock surfaces are erratic and large voids are typically present. They can typically be designed to resist compression, uplift and lateral loads and have been used to support a variety of facilities. Installation techniques can be tailored to ensure minimal damage to existing foundations and to allow facility operations to be maintained during construction. Micropiles are often used to support very large capacities with little or no movement of the foundation.
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