A micropile is a high capacity pile created by drilling a small diameter, heavy walled pipe (5/8 inch to 1 inch) into the ground and then grouting (almost always pressure grouting) the lower portion of the pile. Micropiles are usually 7 to 12 inches in diameter. They are capable of carrying loads in the range of 150 kips to over 1000 kips each, (which though very rare has been achieved).
Micropiles are usually but not always grouped under a unifying pile cap. Recent advances in the capacity of the equipment used in installation now allows for the construction of larger pile diameters with corresponding increased capacity. These piles are quite expensive per foot when compared to other methods of piling. They are used to overcome heavy concentrations of boulders or, in that they are usually installed with low headroom rigs, they are often used in cases of limited headroom. They are also used in earth retention and slide repair applications.*
* The above definition is based on information provided by Alan Macnab, P. ENG, D. GE. Macnab is the author of the “Earth Retention Handbook”, (McGraw-Hill), a leading text in the deep foundations and earth retention industries. He provides design and construction consulting services to the referenced industries. He can be reached at: firstname.lastname@example.org
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