Experimental Modeling and Numerical Simulation of Lateral Spreading for Validation of Constitutive Models PDF Download

Author: Trevor James Carey
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ISBN: 9781658412421
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Languages : en
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Book Description
Numerical modeling is often relied on as the most advanced approach for predicting the effects of liquefaction for complex geosystems. While numerical methods are often used to model seismic performance, little is known about how accurately constitutive models capture the physics behind liquefaction. The Liquefaction Experiments and Analysis Projects (LEAP) is an international effort among numerical and physical modelers to validate numerical models used to predict the effects of liquefaction. LEAP is conducted over a series of phases, or projects, each addressing a specific component of the overall goal of validation. The research in this dissertation presents components of LEAP, considering both experimental and numerical modeling of liquefaction. The overall goals are to: 1) provide high quality experimental data for validation of numerical constitutive models and 2) demonstrate the behavior and sensitivity of commonly used numerical liquefaction models. The goal of the first major US phase of LEAP, LEAP-GWU-2015, was to repeat the same centrifuge experiment at different research facilities, to serve as a single point for validation. The experiment consisted of a submerged slope of uniform sand. The centrifuge experiment performed at UC Davis as a part of the LEAP-GWU-2015 phase is discussed, including the experiment results, novel testing procedures, modifications to the model container, and nonconformities with experiment specifications. Prior to the second major LEAP phase, new centrifuge testing equipment was developed to characterize the initial conditions of the experiment and model response during liquefaction. A low-cost cone penetrometer device was designed and distributed to the LEAP testing facilities for improved quality control. A linear regression is presented that uses measured cone tip stresses to correct reported initial densities from mass and volume measurements. A novel hardware configuration to measure liquefaction induced deformations of a submerged slope was developed. The new configuration records displacements using five GoPro cameras attached to a submerged clear acrylic window located above the slope, which acts as a glass-bottom boat to avoid distortion due to water surface waves. The highspeed videos recorded during shaking are converted to images and using GEO-PIV displacements time histories are calculated. Time series displacements measured with the new hardware configuration were shown to produce comparable results as hand measurements and sensor data. The second major LEAP phase, LEAP-UCD-2017, consisted of twenty-four centrifuge experiments performed at nine research facilitates using the same testing geometry as the LEAP-GWU-2015 exercise. The new strategy of the LEAP-UCD-2017 phase was to intentionally vary the key input variables of motion intensity and soil density to determine the sensitivity of residual displacements to these variables. The three centrifuge experiments performed at UC Davis for LEAP-UCD-2017 are presented, including the experiment results, new procedures to estimate model specimen density, and minor nonconformities with experimental specifications. Following the LEAP-UCD-2017 and LEAP-ASIA-2019 phases an experimental displacement response surface that relates soil density, input motion intensity, and slope displacement was developed using nonlinear regression analysis of the centrifuge test data. A numerical response surface was developed using the PDMY02 constitutive model using the OpenSees finite element framework. The PDMY02 model was calibrated for three relative densities using available cyclic element test laboratory data; after considerable effort the triggering curves (cyclic stress ratio vs number of cycles to liquefaction) for the PDMY02 model cross the triggering curves developed from laboratory data, but the shapes of the numerical curves do not match the laboratory curves. A finite element mesh of the LEAP-UCD-2017 centrifuge test geometry was developed and the displacement response surface for the PDMY02 model was developed by varying the intensity of the input motion for the three calibration densities. The resulting numerical response surface is shown to match the experimental surface well, despite the fact that the numerical liquefaction triggering curves are not a good fit with the laboratory liquefaction triggering curves. Together, the results presented in this dissertation contribute to our understanding of numerical model validation and help to reconcile the different inferences produced through numerical modeling and centrifuge experiments.