Seismic Response of Multi-Story Structure Strengthened with Micropiles

Micropiles are reinforced grouted piles that have small diameters commonly not higher than 30 cm. They are widely used for slope stabilization, controlling structural settlement, and in some cases, as retaining structures. Also, they are used for resisting dynamic uplift loads, seismic retrofit mainly in restrictive and low headroom areas, and retrofitting of historical monuments. The main goal of this research is to develop a finite element model that can capture the different aspects of seismic behavior of multi-story structure supported with deep foundation via using of micropiles. Also, a main target for the executing numerical modelling is to show the influence of the surrounding soil on this system and vice versa. Firstly, a representative two-dimensional finite element model is conducted to represent the soil-structure interaction system under seismic excitation supported with proper boundary conditions in PLAXIS 2D V20 for dynamic analysis based on previous recommendations considering the nonlinear soil behavior. The behavior of micropiles is studied and verified using previous results. Based on these models, the effect of lateral dynamic loads on the response of a structure with different foundation types is investigated. Also, a wide range of parametric studies, considering structure properties, earthquake magnitude, micropile diameter, micropile length, and the number of micropiles, have been carried out in order to investigate the actual interaction between soil, substructure, and superstructures. The study results showed that the seismic response of the structure is highly affected by the properties of the sub-surface soil layer. Consequently and similarly, analysis results established that underpinning using micropiles is an efficient technique for controlling the seismic response of existing structures.