Volume 7, Issue 1, January 2013
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Grouted Micropiles for Foundation Remediation in Expansive Soil (8th Michael W. O'Neil Lecture)
John D. Nelson, Ph.D., P.E., D.GE.; Kuo-Chieh Chao, Ph.D., P.E.; Daniel D. Overton, M.S., P.E.; Zachary P. Fox, M.S.; and Jesse S. Dunham-Friel, M.S., P.E.
Foundation underpinning is a common component of remediation schemes for distressed foundations on expansive soils. For many applications in expansive soil, micropiles have distinct advantages over other techniques. This paper will concentrate on the design and construction of micropiles in expansive soil. It discusses the nature of building distress and the relationship between foundation movement and soil heave. It presents methods for determining the factors that are required for the design of micropiles. Such factors include calculation of expected free-field heave, depth of soil wetting, and prediction of pier movement. A finite element program developed by the authors and others to determine pier heave and internal forces is presented. The input parameters that are required for pier analysis are discussed, and the nature of the output and the sensitivity of the results to the output are described. A case example illustrates the advantages of micropiles over other methods.