Liquefaction-targeted Ground Motion Parameters PDF Download

Author: Andrew J. Makdisi
Publisher:
ISBN:
Category :
Languages : en
Pages : 340

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Book Description
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.