PERFORMANCE-BASED SEISMIC EVALUATION OF SINGLE PILE AND PILE GROUPS IN LAYERED SOIL USING PLAXIS 3D

The analysis of a single pile in layered soil shows that the bending moment varies along the depth due to changes in soil properties. The maximum bending moment of about +2.642 kNm occurs at –9 m to –10 m, while the minimum value of about –1.675 kNm is observed near –2 m in soft clay. This indicates that softer soil allows more deformation, while stiffer layers resist movement and create higher bending at certain depths. From the sensitivity study, it is observed that soil stiffness and earthquake duration have major influence on pile response. Softer soil increases bending moment, while higher stiffness reduces deformation but increases force transfer. The damping ratio (1% to 5%) shows very little effect on results. Increasing earthquake duration increases bending moment up to 3.469 kNm due to repeated loading. Lowering the water table from 0 m to –5 m reduces displacement but increases bending moment up to 6.192 kNm due to increased soil stiffness. The comparison between single pile and 2×2 pile group shows that the pile group experiences much higher bending moment (13.85 kNm) compared to single pile (0.876 kNm), with maximum value near the pile head due to pile cap and group interaction. At the same time, displacement is much lower in the pile group (10⁻⁹ m) compared to single pile (10⁻⁶ m), showing higher stiffness and stability. Overall, pile groups reduce movement but increase internal forces, so proper design is required under seismic loading.

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