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The use of micropiles has grown significantly since their conception in the 1950s, and in particular, since the mid-1980s. Micropiles have been used mainly as elements for foundation support to resist static and seismic loading conditions, and as in-situ reinforcements for slope and excavation stability. Many of these applications are for transportation structures.
Piles are divided into two general types - displacement piles and replacement piles. Displacement piles are members that are driven or vibrated into the ground, thereby displacing the surrounding soil laterally during installation. Replacement piles are placed or constructed within a previously drilled borehole, thus replacing the excavated ground. A micropile is a small-diameter (typically less than 12 inches), drilled and grouted replacement pile that typically is reinforced. A micropile is constructed by drilling a borehole, placing reinforcement, and grouting the hole. Micropiles can withstand axial and/or lateral loads, and may be considered a substitute for conventional piles or as one component in a composite soil/pile mass, depending upon the design concept employed.
Micropiles are installed by methods that cause minimal disturbance to adjacent structures, soil and the environment. They can be installed in access-restrictive environments and in all soil types and ground conditions. Micropiles can be installed at any angle below the horizontal using the same type of equipment used for ground anchor and grouting projects. Since the installation procedure causes minimal vibration and noise, and can be used in conditions of low headroom, micropiles often are used to underpin existing structures. Specialized drilling equipment often is required to install the micropiles from within...