Effect of Site Parameters on Dynamic Impedance of Bridge Piles Subjected to Seismic Loading

Dynamic impedance of pile groups is dependent on soil parameters, i.e. soil unit weight (ρ _s ), Poisson’s ratio (ν), shear modulus (G _s ), shear wave velocity (V _s ) and damping ratio (β _s ). The last three soil parameters (G _s , V _s & β _s ) strongly depend on the strain level caused by propagating seismic waves. Near surface (30 m depth) values of soil design parameters (G _s , V _s & β _s ) are normally used in design and these are influenced by variation in soil properties like plasticity index (PI), over consolidation ratio (OCR), effective stress (σ’), depth of soil strata over bedrock (H) and impedance contrast ratio (ICR) between the strata and the bedrock. The aim of this study was to investigate the sensitivity of dynamic pile-group impedance to variation in soil design parameters (G _s , V _s & β _s ) caused by variation in soil properties for a typical bridge that was founded in site classes C and D according to the AASHTO Code and were subjected to a suite of actual earthquake ground motions.