2D ANALYSIS OF THE SEISMIC BEHAVIOR OF INCLINED MICROPILES-Paper

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The study uses two-dimensional dynamic finite-element analysis in PLAXIS to examine how micropile inclination affects the seismic response of a soil–micropile–structure system. Micropiles are modeled as elastic beam elements, the superstructure as a single-degree-of-freedom column with concentrated mass, and damping as Rayleigh damping. Harmonic base excitation is applied with absorbing lateral boundaries.<br /><br />Two soil profiles are considered: homogeneous soil with constant stiffness and soil whose stiffness increases with depth. In both cases, increasing micropile inclination generally reduces seismic demand. In homogeneous soil, greater inclination lowers horizontal soil acceleration and reduces structure and cap acceleration amplification. It also substantially decreases peak pile-head shear; at 20° inclination, shear is 75% below that for vertical micropiles. In the increasing-stiffness profile, 20° inclination reduces peak shear by 90%. Inclination also diminishes secondary shear and bending-moment peaks, while distributing axial forces more consistently along the piles.<br /><br />The structure’s acceleration amplification is approximately 30–40% greater than the cap’s in both soil profiles, highlighting the importance of including structural dynamic amplification in seismic evaluation. Responses in the depth-varying soil are more complex: soil acceleration does not decrease uniformly as inclination increases, so an optimal angle is needed.<br /><br />Overall, the numerical results indicate that inclined micropiles can improve seismic performance by reducing bending moments, shear forces, and superstructure amplification. The benefit depends on soil stiffness variation and pile angle; the study therefore supports selecting inclination based on site-specific soil conditions.

Keywords

micropile inclination

seismic response

finite-element analysis

PLAXIS

soil-structure interaction

harmonic base excitation

Rayleigh damping

bending moment

shear force

soil stiffness profile