Dissertation/Thesis Abstract

Site Response Analyses of Liquefiable Soil Profiles Under Multiple Shaking Events: Validation of Numerical Models Against Centrifuge Model Tests
by Alshawaf, Hussain A A A, M.S., University of California, Davis, 2020, 146; 28000380
Abstract (Summary)

Liquefaction is a major earthquake-induced hazard that has been studied extensively through the years but still poses significant challenges to researchers and practitioners, even for level-ground free-field conditions. Case histories, laboratory tests at different scales, from bench-level to full scale shaking table tests, as well as advanced numerical modeling have provided insights into the phenomenon of liquefaction triggering as well as its effects on infrastructure. The ability of numerical tools to capture liquefaction behavior and responses is of particular importance for our ability to further investigate case histories and large scale experimental data, as well as predict and design for future scenarios.

In this study, a one-dimensional site response analysis (SRA) model is validated against a well-instrumented reference centrifuge model test performed at the UCD-CGM 9 m centrifuge. The model represents a free-field deposit with three distinct layers of soil: liquefiable Ottawa F-65 sand, dense Monterey O-30 sand, and gravel. Numerical simulations are performed in the finite difference commercial platform FLAC (Itasca 2016) and use the stress-ratio controlled, critical state compatible, bounding surface plasticity model for sand, PM4Sand, developed by Boulanger and Ziotopoulou (2017) to capture the response of liquefiable soils.

The numerical model is initially validated against the recorded experimental results for the first shaking event imposed to the centrifuge model. Acceleration time histories, spectral accelerations, Fourier Amplitude Spectra, excess pore pressure time histories, shear stress-strain responses, and transfer functions are tracked in the analyses and are used as metrics to validate the model’s response against the centrifuge model test results. Conclusions are drawn from this phase with regards to discrepancies that were observed, as well as element- and system- level calibrations that improved the predictions.

Following the validation for the first shaking event, the model is subjected to a sequence of multiple input motions from the centrifuge, allowing for time for reconsolidation in-between the events. This sequential analysis gauges how the model’s response performs against the experimental results when simulating cycles of loading-reconsolidation-reloading. The goal of this study is to evaluate the ability of the employed engineering procedures and numerical modeling protocols to capture the experimentally observed results as well as parametrically investigate the sensitivities of the response to selected parameters, providing insights on pathways of improvement for numerical modeling.

Indexing (document details)
Advisor: Ziotopoulou, Katerina
Commitee: Boulanger, Ross W., DeJong, Jason T.
School: University of California, Davis
Department: Civil and Environmental Engineering
School Location: United States -- California
Source: MAI 82/2(E), Masters Abstracts International
Source Type: DISSERTATION
Subjects: Civil engineering, Soil sciences, Geophysics
Keywords: Centrifuge, Liquefaction, Multiple Shaking Events, PM4Sand, Site Response Analysis
Publication Number: 28000380
ISBN: 9798664727869
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