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Pages 1-12

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From page 1...
... This report 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.
From page 2...
... Practitioners now must choose among multiple methods without necessarily understanding their limitations. The current state of knowledge is limited regarding liquefaction triggering assessment associated with, for example, the degree of saturation below the groundwater table, at large depths, beneath sloping ground, in gravelly soils, in soils with a significant component of fine-grained particles (i.e., silt and clay)
From page 3...
... . The committee was tasked to evaluate the following: the sufficiency, quality, and uncertainties associated with laboratory and in situ field tests, case history data, and physical model tests for understanding liquefaction triggering and post-triggering soil behavior; methods to analyze the data from those tests; and the adequacy and accuracy of empirical and mechanistic methods to evaluate triggering and resulting deformations in the soil and the structures built in, on, and of those soils.
From page 4...
... greater than about 15 meters, for earthquake magnitudes less than approximately 5.9 and greater than approximately 7.8, and for cases where liquefaction may reasonably have been expected but was not observed. The Simplified Stress-Based Approach for Assessing Liquefaction Triggering Several empirical liquefaction triggering relationships that are derived primarily from the case history data are applied to liquefaction assessments conducted with the simplified stress-based approach.
From page 5...
... Significant reduction in uncertainties associated with the various adjustment factors used in the simplified approach is most dependent on expansion and improvement of the case history database, but mechanics-based methods can be used where data are insufficient. Alternative Approaches to Liquefaction Assessment Methods other than the simplified stress-based approach to assess liquefaction triggering include a cyclic strain-based alternative to the cyclic stress-based approach, energy-based approaches, laboratory tests and physical models, and computational mechanics-based methods.
From page 6...
... To be compatible with current developments in other areas of earthquake engineering (e.g., performancebased design of structures) , the practice of liquefaction assessment needs to move toward fully probabilistic analyses that incorporate the complete range of possible damaging earthquake ground motions (in terms of both ground motion intensity and earthquake magnitude)
From page 7...
... PLHAs are well developed for liquefaction triggering and recently have been extended to consequences such as lateral spreading and post-earthquake free-field settlement. They have also been used to show that estimates of actual liquefaction hazards using current procedures as applied in practice can be highly inconsistent.
From page 8...
... CPT results are less dependent on the equipment operator or setup than most other in situ test methods, and CPT can be performed with relative speed and economy. It may also be prudent to conduct one or more SPT borings in addition to CPT soundings to provide physical samples for soil characterization as well as to provide an additional means of liquefaction potential assessment.
From page 9...
... Identifying and, if possible, quantifying the uncertainty associated with each adjustment factor, empirical correlation, and parameter relationship used in a liquefaction assessment will help to avoid the compounding of uncertainties and to facilitate assessment of the overall uncertainty associated with the method. When developing a liquefaction triggering or consequence assessment method, using adjustment factors, empirical correlations, and parameter relationships with builtin bias will compound uncertainties and make it difficult, if not impossible, to assess the overall uncertainty associated with the method -- an important consideration in liquefaction assessments.
From page 10...
... Regional variations in seismicity, coupled with the significant uncertainties in earthquake loading and liquefaction resistance, warrant probabilistic characterization for the evaluation of both the hazards of liquefaction triggering and the risk of liquefaction triggering. The geotechnical community needs to develop PLHAs to meet the growing demand from the greater earthquake engineering community for risk-based liquefaction assessment as part of the trend toward performance-based design.
From page 11...
... Conduct fundamental research on the stress, strain, and strength behaviors of soils prior to and after liquefaction triggering; devise new laboratory and physical model experimental techniques to aid development of constitutive models of those behaviors. Advancing the state of the art and practice in liquefaction assessment requires fundamental research on liquefaction phenomena, both theoretical and experimental, because the stress-strain
From page 12...
... Researchers can provide more high-quality field case history data supplemented with laboratory and model test data as well as more accurate models to assess earthquake-induced soil liquefaction. Practitioners need to better understand the limitations of characterization and assessment approaches and the geologic and tectonic controls on liquefaction hazards at their sites.


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