Micropiles are grouted and small diameter piles that are traditionally used in foundation retrofit. Experimental evidence has indicated that micropiles behave well under seismic loading due to their high flexibility. Moreover, observations in the 1995 Kobe Earthquake indicate a good performance of friction piles under seismic loading. However, the seismic behavior of micropiles is not fully understood due to the limited number of full- and model-scale tests, as well as the limited amount of numerical modeling studies for micropiles.
This project focuses on Finite Element modeling (FEM) of single micropile and micropile groups under both static and dynamic loading. Initially, dynamic FE soil models were developed to conduct site response analyses. The lateral vertical boundaries of the soil were set up in such a way that the reflection of the arrival waves at the boundaries was avoided. The results of the site response analyses were verified against the well-validated code, SHAKE. Subsequently, FE models for micropiles were developed with two constitutive soil models, i.e. a linear elastic and a bounding surface plasticity model. The micropile/soil interface was modeled either with perfect bonding or with frictional interface elements. For dynamic loading cases, a SDOF (single degree-of-freedom) superstructure was placed on top of the micropiles. Parametric studies were performed for various independent variables including load intensity, non-linearity of soil, and soil stiffness for the static case; and soil non-linearity, input motion intensity, frequency contents of input motion, and the natural period of the superstructure for the dynamic case. The static and dynamic behavior of micropiles was studied via the effects of aforementioned independent variables on the deflections and bending moments along the micropile length.