Seismic site response analysis of liquefiable soil deposits focusing on the ground surface response spectrum: Fid-Bau Portal

Seismic site response analysis of liquefiable soil deposits focusing on the ground surface response spectrum

Anthi, M. / Gerolymos, N.

Abstract A numerical algorithm is developed for conducting one-dimensional non-linear ground response analysis of layered sites, capable of reproducing liquefaction phenomena and accounting for the simultaneous dissipation of excess pore water pressure through soil grains. Τhe shear wave propagation algorithm is based on the plasticity constitutive model for sand Ta-Ger, expressed in a one dimensional p-q space form. This model demonstrates remarkable versatility in representing complex patterns of the cyclic behavior of sand, such as stiffness decay and strength reduction due to pore-water pressure buildup. The calibration of the model is based on shear modulus reduction and damping curves for drained loading conditions, as well as liquefaction resistance curves for undrained conditions. A detailed presentation of the numerical model formulation is provided, outlining the numerical approach for solving the wave propagation and consolidation differential equations. To validate model predictions, the recorded seismic ground response of the Port Island array during the 1995 Kobe earthquake is utilized. Furthermore, the model is applied to estimate the elastic response spectra at the surface of soil profiles with liquefiable layers (ground type S 2) as per EC8:2004. The investigation involves the ground response analysis of various soil p3rofiles, all including a liquefiable zone, excited by a suite of earthquake motions at their base. The acceleration time histories are extracted from the PEER Ground Motion Database, having characteristics compatible with the NGA-estimated response spectrum at the bedrock as well as key seismological parameters such as the earthquake magnitude M w and the horizontal distance from the fault R JB. Two different methods are employed for selecting the base excitations: amplitude-scaled records to match a target response spectrum and spectral-matched records. From the results, an idealized response spectrum is derived in terms of the design spectrum parameters S, η, Τ Β and T C . The findings demonstrate that the idealized ground surface response spectrum is minimally sensitive to the method used for base excitation selection.

Highlights • Constitutive model and wave propagation Algorithm for 1D site response analysis of layered deposits with consolidation. • Verification through comparison with analytical expressions emphasizing on pore-water pressure dissipation. • Validation through comparison against the case history of Port Island array in Kobe 1995 earthquake. • Novel methodology for site response analysis of liquefiable deposits to determine the elastic response spectra at surface. • Determination of standardized response spectra for design purposes.