NUMERICAL EVALUATION OF GROUNDWATER-LEVEL EFFECTS ON THE SEISMIC RESPONSE OF A MULTISTORY BUILDING–SOIL SYSTEM USING PLAXIS 3D

Abstract

Groundwater conditions can alter the effective stress state and mass characteristics of foundation soils and thereby influence seismic soil–structure interaction. This study evaluated the effect of groundwater level (GWL) on the seismic response of a multistory building–soil system using three-dimensional finite-element modeling in PLAXIS 3D. The computational domain comprised three soil layers extending from the ground surface to a depth of 50 m and represented by the Mohr–Coulomb constitutive model under drained conditions. Two controlled models were analyzed with GWLs of −50 m and −3 m. Geometry, material properties, the building model, finite-element mesh, monitoring locations, and the same 0–10 s real earthquake accelerogram were held constant so that groundwater level was the only intentionally varied condition. Horizontal displacement, velocity, and acceleration time histories were compared at a soil monitoring node and at the first and ninth floors. The maximum downward vertical displacement was −48.37 mm and was concentrated within the foundation influence zone. At the soil node, several velocity and acceleration peaks were larger for GWL = −3 m, whereas horizontal displacement histories were nearly coincident. First-floor responses were similar between cases, while ninth-floor acceleration exceeded first-floor acceleration. The findings indicate that groundwater level should be treated as an independent variable in seismic soil–structure interaction analyses and that acceleration and velocity may be more sensitive to groundwater changes than displacement under the modeled conditions.