This volume presents select papers presented at the 7th International Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics. The papers discuss advances in the fields of soil dynamics and geotechnical earthquake engineering. Some of the themes include ground response analysis & local site effect, seismic slope stability and landslides, application of AI in geotechnical earthquake engineering, etc. A strong emphasis is placed on connecting academic research and field practice, with many examples, case studies, best practices, and discussions on performance based design. This volume will be of interest to researchers and practicing engineers alike.
TRB’s National Cooperative Highway Research Program (NCHRP) Synthesis 428: Practices and Procedures for Site-Specific Evaluations of Earthquake Ground Motions identifies and describes current practice and available methods for evaluating the influence of local ground conditions on earthquake design ground motions on a site-specific basis.
This collection contains 15 invited and contributed papers focusing on the the behavior of silty and gravelly soils under seismic loading presented at sessions of the ASCE National Convention, held in Atlanta, Georgia, October 9-13, 1994.
The August 17, 1999, Kocaeli, Turkey earthquake (Mw = 7.4) struck the northwestern region of the country and was one of the most deadly and costly earthquakes of the country's modern history. Ground failure in Adapazari was particularly severe. Besides pervasive structural damage, hundreds of buildings settled, tilted, and translated horizontally over their foundations. Ground failure was observed predominantly directly adjacent to buildings. The primary goals of this dissertation are to explain the causes of the ground failures and their resulting effect on building performance in Adapazari. The investigation focuses initially on: 1) the characterization of the buildings at twelve sites where ground failure was observed, and 2) the characterization of the subsurface soil conditions that exist under the foundation of these buildings. The subsurface investigation program included Cone Penetration Test (CPT) soundings and carefully performed soil borings with the implementation of the Standard Penetration Test (SPT). The energy imparted to the system by the drop of the hammer during the SPT was measured to obtain accurate values of N6o. Additionally, the observations at areas of the center of the city where ground failure did and did not occur after the Koceali earthquake were correlated with the liquefaction susceptibility of the subsurface soils. The in situ testing program found that the soils that led to severe building damage are shallow, Holocene, low to medium plasticity alluvial silts. The response of these soils to earthquake shaking is less understood than that of clean sands. Thus, the second task of this investigation was to obtain representative "undisturbed" specimens of these soils and test them under cyclic loading in the laboratory. This required establishing a cyclic triaxial device in Turkey to avoid the disturbance associated with shipping soils back to the USA. The results of a large number of cyclic tests (primarily triaxial with some simple shear) showed that the current state-of-the-art method for evaluating liquefaction susceptibility of fine-grained soils, i.e. the Chinese Criteria, is not reliable. A new procedure for the identification of fine-grained soils susceptible to liquefaction and cyclic mobility based on the soil's plasticity index and liquid limit to water content ratio was developed. The results of the cyclic tests were also used to evaluate the liquefaction triggering potential of Adapazari silt. The results of this analysis were compared with those obtained from the use of in situ tests, and were found to be generally consistent. The additional confinement and loading of the buildings in Adapazari were found to significantly reduce the shallow silt's resistance to liquefaction and increase the shear strain induced by the earthquake. The ground motions to which the buildings in downtown Adapazari might have been subjected to and the possible mechanisms that led to the observed building performance are explained in a general framework.
Ground motion intensity measures are used to represent various components of earthquake shaking intensity and frequency content in the form of simple parameters; examples include peak ground acceleration, Arias intensity, and pseudo-spectral acceleration (PSA). Ground motion models (GMMs) are developed to predict these intensity measures as a function of earthquake source, wave propagation path, and local geotechnical site conditions. GMMs are formulated to capture the underlying physics of source processes, wave propagation, and site response, with individual model parameters set based on various combinations of empirical ground motion data analysis and physics-based ground motion simulations. The majority of GMMs are conditioned for hard rock reference sites, with shear wave velocity (VS) = 3000 m/s, or with a time-averaged shear wave velocity in the upper 30 meters of the crust (VS30) = 760 m/s. Additional site amplification models are necessary in order to estimate GMIMs for other site conditions, including weathered rock and soil sites. As shear waves propagate vertically in the near-surface, the conservation of energy dictates that the wave amplitude must increase as the seismic velocity of the medium decreases. This amplification, or the so-called linear site effect, is usually parameterized using VS30, and sometimes site fundamental frequency or depth to bedrock, if available. This thesis has two parts, according to subject matter. The first part of this thesis, consisting of Chapters 2, 3, and 4, focuses on seismic site characterization and site amplification in central and eastern North America (CENA) in the context of the Next Generation Attenuation-East (NGA-East) project. Chapter 2 presents a hybrid geology-slope approach for VS30 estimation that utilized a new and expanded shear-wave velocity (VS) measurement database for CENA. The proxy is conditioned on geologic category from newly considered large-scale geologic maps, the extent of Wisconsin glaciation, sedimentary basin structure, and 30 arc-sec topographic gradient. Nonglaciated sites were found to have a modest natural log dispersion of VS30 ( ln V= 0.36) relative to glaciated sites ( lnV = 0.66), indicating better predictability of VS30 for the former. These findings were used estimate the mean and standard deviation of VS30 for NGA-East recording stations when measurements were not available. Chapter 3 presents empirical linear site amplification models conditioned on time-averaged shear wave velocity in the upper 30 m (VS30) for CENA, developed using a combination of least-squares, mixed effects, and Bayesian techniques. Site amplification is found to scale with VS30 for intermediate to stiff site conditions (VS30 > 300 m/s) in a weaker manner than for active tectonic regions. For stiff sites (> 800 m/s), I find differences in amplification for previously glaciated and non-glaciated regions, with non-glaciated sites having lower amplification. The models account for predictor uncertainty, which does not affect the median model, but decreases model dispersion. Lastly, Chapter 4 presents recommendations for modeling of ergodic site amplification in CENA, based primarily on results from the literature (including the model in Chapter 3), for application in the U.S. Geological Survey national seismic hazard maps. Previously, the maps have used site factors developed using data and simulations for active tectonic regions; however, results from NGA-East demonstrate different levels of site amplification in CENA. The recommended model has three terms, two of which describe linear site amplification: an empirically constrained VS30-scaling term relative to a 760 m/s reference, and a simulation-based term to adjust site amplification from the 760 m/s to the CENA reference of VS = 3000 m/s. The second part of this thesis, consisting of Chapters 5 and 6, focuses on the development of a global GMM and site amplification model with regional adjustment factors for subduction zone regions as a part of the Next Generation Attenuation-Subduction (NGA-Sub) project. Chapter 5 presents global subduction zone GMMs for interface and intraslab events, with regionalized terms for Alaska, Cascadia, Central America. Mexico, Japan, South America, and Taiwan. The near-source saturation model, magnitude-dependent geometrical spreading, and magnitude-scaling break point are constrained using simulations and fault geometry, and the anelastic attenuation, magnitude scaling, and depth scaling terms are constrained empirically. The model is regionalized in the constant, anelastic attenuation, and depth-scaling terms, and the magnitude break-point. When applying the model to a region not considered in the study, we recommend using an appropriate range of epistemic uncertainty that captures regional variation. Chapter 6 presents a subduction-specific site amplification model, meant to be paired with the reference-rock GMM of Chapter 5. This site amplification model for subduction regions accounts for regional differences in VS30-scaling, and re-calibrates a widely used nonlinear site term for active tectonic regions.
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.
