Effects of Long-duration Ground Motions on Liquefaction Hazards

Effects of Long-duration Ground Motions on Liquefaction Hazards
Author: Michael W. Greenfield
Publisher:
Total Pages: 451
Release: 2017
Genre:
ISBN:
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Soil liquefaction during past earthquakes has caused extensive damage to buildings, bridges, dam, pipelines and other elements of infrastructure. Geotechnical engineers use empirical observations from earthquake case histories in conjunction with soil mechanics to predict the behavior of liquefiable soils. However, current empirical databases are insufficient to evaluate the behavior of soils subject to long-duration earthquakes, such as a possible Mw = 9.0 Cascadia Subduction Zone earthquake. The objective of this research is to develop insight into the triggering and effects of liquefaction due to long-duration ground motions and to provide recommendations for analysis and design. Recorded ground motions from 21 case histories with surficial evidence of liquefaction showed marked differences in soil behavior before and after liquefaction was triggered. In some cases, strong shaking continued for several minutes after the soil liquefied, and a variety of behaviors were observed including dilation pulses, continued softening due to soil fabric degradation, and soil stiffening due to pore pressure dissipation and drainage. Supplemental field and laboratory investigations were performed at three sites that liquefied during the 2011 Mw = 9.0 Tohoku earthquake. The recorded ground motions and field investigation data were used in conjunction with laboratory observations, analytical models, and numerical models to evaluate the behavior of liquefiable soils subjected to long-duration ground motions. Observations from the case histories inspired a framework to predict ground deformations based on the differences in soil behavior before and after liquefaction has triggered. This framework decouples the intensity of shaking necessary to trigger liquefaction from the intensity of shaking that drives deformation by identifying the time when liquefaction triggers. The timing-based framework promises to dramatically reduce the uncertainty in deformation estimates compared to conventional, empirically-based procedures.

State of the Art and Practice in the Assessment of Earthquake-Induced Soil Liquefaction and Its Consequences

State of the Art and Practice in the Assessment of Earthquake-Induced Soil Liquefaction and Its Consequences
Author: National Academies of Sciences, Engineering, and Medicine
Publisher:
Total Pages: 350
Release: 2019-01-30
Genre:
ISBN: 9780309440271
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Earthquake-induced soil liquefaction (liquefaction) is a leading cause of earthquake damage worldwide. Liquefaction is often described in the literature as the phenomena of seismic generation of excess porewater pressures and consequent softening of granular soils. Many regions in the United States have been witness to liquefaction and its consequences, not just those in the west that people associate with earthquake hazards. Past damage and destruction caused by liquefaction underline the importance of accurate assessments of where liquefaction is likely and of what the consequences of liquefaction may be. Such assessments are needed to protect life and safety and to mitigate economic, environmental, and societal impacts of liquefaction in a cost-effective manner. Assessment methods exist, but methods to assess the potential for liquefaction triggering are more mature than are those to predict liquefaction consequences, and the earthquake engineering community wrestles with the differences among the various assessment methods for both liquefaction triggering and consequences. State of the Art and Practice in the Assessment of Earthquake-Induced Soil Liquefaction and Its Consequences evaluates these various methods, focusing on those developed within the past 20 years, and recommends strategies to minimize uncertainties in the short term and to develop improved methods to assess liquefaction and its consequences in the long term. This report represents a first attempt within the geotechnical earthquake engineering community to consider, in such a manner, the various methods to assess liquefaction consequences.

Hazard Analysis of Seismic Soil Liquefaction

Hazard Analysis of Seismic Soil Liquefaction
Author: Yu Huang
Publisher: Springer
Total Pages: 180
Release: 2017-04-11
Genre: Science
ISBN: 9811043795
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This book presents comprehensive hazard analysis methods for seismic soil liquefaction, providing an update on soil liquefaction by systematically reviewing the phenomenon’s occurrence since the beginning of this century. It also puts forward a range of advanced research methods including in-situ tests, laboratory studies, physical model tests, numerical simulation, and performance-based assessment. Recent seismic liquefaction-related damage to soils and foundations demonstrate the increasing need for the comprehensive hazard analysis of seismic soil liquefaction in order to mitigate this damage and protect human lives. As such the book addresses the comprehensive hazard analysis of seismic soil liquefaction, including factors such as macroscopic characteristics, evaluating the liquefaction potential, dynamic characteristics and deformation processes, providing reliable evaluation results for liquefaction potential and deformation in the context of risk assessment. “p>

Liquefaction-targeted Ground Motion Parameters

Liquefaction-targeted Ground Motion Parameters
Author: Andrew J. Makdisi
Publisher:
Total Pages: 340
Release: 2021
Genre:
ISBN:
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Earthquake-induced ground failure, resulting from liquefaction of loose sand and soft clay deposits, has caused tremendous damage to the built and natural environment. Ground failures due to lateral spreading, an effect of soil liquefaction at sites on mildly sloping ground or in close proximity to natural or man-made free faces, has been observed to pose significant risks to bridge pile foundations, underground utilities, and shallow foundation systems. Conventional design guidelines in the United States are typically centered on analysis of the liquefaction triggering limit state, by computing a factor of safety (FSL) that considers a single, probabilistic level of earthquake ground shaking. When compared with fully probabilistic analyses of liquefaction triggering that consider all levels of ground shaking, conventional analyses may result in inconsistent representations of the actual liquefaction hazard in different regions of the U.S. Furthermore, analyses that focus on the triggering limit state, rather than the effects of liquefaction (i.e. ground deformations), are generally insufficient in predicting physical damage and losses, particularly in probabilistic frameworks. In this study, a computational platform for fully probabilistic liquefaction hazard analysis (PLHA) is developed and utilized to evaluate the degree to which conventional liquefaction hazard analyses deviate from the actual liquefaction hazard for the triggering limit state. A comparison study between PLHA-based and conventional estimates of FSL indicates a large degree of inconsistency both at the regional and national scale, with some parts of the U.S. designing for nearly three times the implied hazard as others when using conventional analyses. To address this inconsistency, a framework is presented for mapping a liquefaction-targeted ground motion intensity measure for a reference soil and site condition, that, in conjunction with site-adjustment factors can be used in conventional analyses to obtain hazard-consistent estimates of FSL. The framework is validated for a range of geographic locations, seismotectonic environments, soil parameters, and site conditions. Finally, recognizing the need to focus on the effects of liquefaction, a large-scale, simulation-based parametric study, consisting of nonlinear finite-element dynamic analyses performed via a high-performance computing platform, is presented for investigating the physical mechanisms that contribute to lateral spreading-type ground failures. The results of this study are used to develop and present a probabilistic framework for predicting post-triggering ground deformations that accounts for the time of liquefaction during during earthquake motions, as well as system-level effects such as the reduction in seismic demands due to liquefaction in deeper soil strata.

Evolutionary Intensity Measures for More Accurate and Informative Evaluation of Liquefaction Triggering

Evolutionary Intensity Measures for More Accurate and Informative Evaluation of Liquefaction Triggering
Author: Samuel S. Sideras
Publisher:
Total Pages: 717
Release: 2019
Genre:
ISBN:
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Soil liquefaction is a seismic hazard that can have a devastating effect on the stability of buildings, bridges, dams, and other critical infrastructure elements. Accurate evaluation of liquefaction hazards requires accurate evaluation of the potential for triggering of liquefaction, and its effects. A recently developed framework for evaluation of liquefaction hazards considers the timing of the liquefaction process, and requires consideration of the response of liquefiable soils to transient loading histories - an aspect of behavior of liquefiable soils that has not previously been quantified. The development of this framework served as the motivation for the current study. Specifically, the goal of this study was to evaluate evolutionary intensity measures, or measures of the earthquake loading that build up with time over the duration of the ground motion, for prediction of the initiation of liquefaction. This represents the critical first step in the timing-based framework. This study used both cyclic simple shear and centrifuge testing to systematically investigate the response of liquefiable soils to fully transient earthquake loading histories. The results of these tests were used to evaluate the efficiency of evolutionary intensity measures that are typically associated with the initiation of liquefaction. In addition, observations from these tests identified key aspects of an earthquake loading history that are closely related to the generation of excess pore pressure and the initiation of liquefaction. These observations were used to develop a new evolutionary intensity measure that was able to predict the pore pressure response from the laboratory test programs more efficiently than existing intensity measures. The insights that were generated by this study offer the potential to dramatically reduce the uncertainty in the prediction of the initiation of liquefaction as compared to the conventional procedures used in current design practice.

Earthquake Ground Motion

Earthquake Ground Motion
Author: Walter Salazar
Publisher: BoD – Books on Demand
Total Pages: 238
Release: 2024-03-06
Genre: Science
ISBN: 0854662219
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Earthquake Ground Motion is a compilation of ten chapters covering tectonics, seismicity, site effects, tsunamis, infrastructure, and instrumentation. It presents state-of-the-art techniques for retrieving rupture models, seismogenic structures, and validation of focal mechanisms. It also presents macroseismic archiving tools for historical and instrumental earthquakes and the fundamentals of seismic tomography. The book describes the site response analysis in 2D and 3D, considering topographic and soil structure interactions, its incorporation in a seismic hazard analysis, and the impact of earthquakes on the cost of reconstruction. The final sections are devoted to the genesis of earthquakes tsunamis, non-seismic tsunamis, and the new role of gyroscopes in rotational seismology.

Soil Liquefaction during Recent Large-Scale Earthquakes

Soil Liquefaction during Recent Large-Scale Earthquakes
Author: Rolando P. Orense
Publisher: CRC Press
Total Pages: 280
Release: 2014-04-15
Genre: Technology & Engineering
ISBN: 1315759411
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Soil Liquefaction during Recent Large-Scale Earthquakes contains selected papers presented at the New Zealand Japan Workshop on Soil Liquefaction during Recent Large-Scale Earthquakes (Auckland, New Zealand, 2-3 December 2013). The 2010-2011 Canterbury earthquakes in New Zealand and the 2011 off the Pacific Coast of Tohoku Earthquake in

Liquefaction-Induced Building Performance and Near-Fault Ground Motions

Liquefaction-Induced Building Performance and Near-Fault Ground Motions
Author: Connor Patrick Hayden
Publisher:
Total Pages: 382
Release: 2014
Genre:
ISBN:
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Recent earthquakes in Chile, New Zealand, and Japan have re-emphasized the damaging consequences of liquefaction on infrastructure. Due to the complexity of the problem and limited well-documented field case histories, liquefaction-induced building settlements are often estimated using empirical correlations developed for free-field sites on level ground that account for post-liquefaction volumetric strains only. Additional effects due to the presence of a structure are not accounted for with these procedures. The earthquake performance of structures founded on liquefiable ground depends on a complex interaction between the soil properties, the ground motion characteristics, and the structural properties. This thesis presents three related research projects that address aspects of the effects of soil liquefaction including near-fault sites. This research thesis is focused on characterizing and selection of near-fault ground motions, geotechnical centrifuge testing of model buildings affected by liquefaction, and the development of field case histories in Chile following the 2010 Maule, Chile earthquake. Earthquake ground motions are important in liquefaction-induced building performance. Ground motions in the near-fault region frequently have intense, double-sided pulses in the velocity-time series that can be very damaging to structures; forward directivity is a leading cause of these pulses. However, pulses do not always occur in the forward directivity region, and some pulses are not caused by forward directivity. The present study used a new, automated algorithm to classify a large database of records as pulse or nonpulse motions. A straightforward model was developed to estimate the proportion of pulse motions as a function of closest site-to-source distance and epsilon of the seismic hazard. Geotechnical centrifuge tests provide valuable insight into the performance of structures affected by liquefaction. An area particularly lacking understanding is the interaction of closely spaced structures subjected to liquefaction. Two well-instrumented centrifuge tests were performed to investigate the response of three types of model structures founded on liquefiable ground in isolated and adjacent configurations. Acceleration, pore water pressure, and settlement measurements indicated that liquefaction-induced settlement of structures depends on a complex interaction of ground motion, soil, and structural characteristics. For the particular scenarios examined in this study, adjacent structures experienced moderately lower foundation accelerations, tended to tilt away from each other, and settled less than isolated structures. The 2010, MW = 8.8, Maule, Chile earthquake caused substantial damage, including liquefaction-induced damage to infrastructure and provides an important opportunity to learn from these field case histories. This project focuses on improved characterization of the subsurface conditions using penetration testing (i.e., SPT and CPT) at a hospital and two bridges that suffered liquefaction-induced damage. The recently constructed hospital has 10 structurally isolated wings varying in height from one to six stories, which provides a unique opportunity to examine the differing response of varying wings. Liquefaction of plastic, silty soils at the hospital resulted in differential settlement, whereas liquefaction of clean, medium-dense sandy soils resulted in lateral spreading and damage to bridge piers.

Effects of Liquefaction on Earthquake Ground Motions

Effects of Liquefaction on Earthquake Ground Motions
Author: James Robert Gingery
Publisher:
Total Pages: 453
Release: 2014
Genre:
ISBN: 9781321516586
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Site amplification studies and building code provisions recognize that soil liquefaction can alter the characteristics of ground shaking at a site. However, guidance as to how the amplitudes of spectral accelerations are modified is lacking. To address this issue, a two-part study is undertaken. In the first part an empirical study of ground motions recorded at liquefaction sites is undertaken. Available recorded ground motions from shallow crustal earthquakes at sites that exhibited evidence of liquefaction are compiled. Analysis of spectral acceleration residuals of the recorded ground motions computed relative to Next Generation Attenuation (NGA) estimates reveal positive bias at longer periods, slight negative bias at intermediate periods, and slight positive bias at short periods. Trends with Vs30, NGA-estimated peak ground acceleration (PGA), and moment magnitude are also observed. A model is developed that removes the initially observed residual bias and reduces uncertainty. The proposed model can be used to adjust NGA-estimated acceleration response spectra to account for the effects of liquefaction on ground shaking. In the second part of this study a series of parametric 1-D site response analyses were performed to provide a much larger synthetic dataset and to study geotechnical parameter that are typically unavailable in the empirical data. An existing constitutive model was rigorously calibrated against a widely-used semi-empirical liquefaction triggering method. The calibrated model was used to perform 2988 site response analysis pairs : one with porewater pressure generation and the other without. The resulting surface spectra are compared in a way that is analogous to the empirical study. Liquefaction amplification factors from the site response analysis results exhibit similar trends with period compared to the empirical data, but their amplitudes are systematically lower. The differences might be attributable to the inability of the 1-D site response analyses to capture 2-D and 3-D effects such as surface waves and basin effects, or possibly shortcomings the in the 1-D model's ability to faithfully represent all salient aspects of 1-D wave propagation under liquefaction conditions. Factors that appear to influence liquefaction amplification the most include whether the input motion is pulse-like or not and the amplitude of ground shaking.