State of the Art and Practice in the Assessment of Earthquake-Induced Soil Liquefaction and Its Consequences (2021) / Chapter Skim
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10 Recommendations
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Pages 190-200
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From page 190... ...
Others are directed at researchers and are intended to advance understanding of liquefaction-related phenomena so that current approaches to assessing liquefaction triggering and its consequences may be improved. Still other recommendations look beyond current approaches toward new assessment methods.
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From page 191... ...
Current databases of consequences of liquefaction -- especially of the residual shear strength of liquefied soil, of lateral spreading displacements, and of the interaction between liquefied soils and man-made structures -- also need to be strengthened. This is particularly true for intermediate density and dense soils where liquefaction effects may be subtle or possibly inconsequential: namely, soils with a normalized CPT tip resistance, qc1-cs, greater than about 85 atm (8.6 MPa)
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From page 192... ...
Important gaps in case history databases could be filled by establishing liquefaction observatories at sites that are well characterized, well instrumented, and strategically located in areas where there is a high probability of earthquake-induced soil liquefaction in coming decades. Detailed high-quality characterization of the pre-earthquake surface and subsurface conditions at field observatories that then capture liquefaction events would strengthen the value of recorded data by removing some uncertainty related to pre-liquefaction soil properties and liquefactioninduced effects (e.g., changes in soil properties and ground displacements)
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From page 193... ...
. Rotary wash borings for SPT testing are more reliable than are hollow stem auger borings, as SPT blow counts recorded in hollow stem auger borings below the water table are particularly susceptible to error and should be carefully evaluated for indications of borehole disturbance (i.e., abnormally low blow count values)
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From page 194... ...
When refining or developing new empirical relationships for use in liquefaction analyses, incorporate unbiased estimates for input parameters; identify and quantify when possible the uncertainty associated with those estimates; and use soil mechanics principles, seismologic principles, and experimental data to extrapolate beyond ranges in which field data constrain the empirical relationships. Relationships for analysis of liquefaction triggering and consequences based on case history data include cyclic resistance curves developed for simplified stress-based analysis of triggering, relationships between post-liquefaction shear strength and penetration resistance, and equations for evaluating the levels of liquefaction-related lateral spreading.
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From page 195... ...
A database of geologic evidence for liquefaction in the central and eastern United States could be expanded worldwide, and it could provide information on the sedimentary environment, depositional age, and tectonic setting to guide evaluation of the influence of these factors on liquefaction potential. This effort, in turn, might enable case history databases to be made more complete by including data on geologic evidence for liquefaction in earthquakes in the 19th century and before.
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From page 196... ...
Descriptions of procedures to evaluate liquefaction do not always state clearly where and what the uncertainties are and typically do not address how to incorporate them into the liquefaction assessment. Furthermore, while many factors used for liquefaction assessment require correction, the correction factors (e.g., corrections applied to SPT blow counts, magnitude scaling
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From page 197... ...
To accomplish this, computational tools need to be integrated with PSHA tools, making certain they allow weighted contributions from multiple predictive models to account for epistemic uncertainty. The geotechnical community needs to develop PLHA 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.
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From page 198... ...
Use experimental data and fundamental principles of seismology, geology, geotechnical engineering, and engineering mechanics to develop new analytical techniques, screening tools, and models to assess liquefaction triggering and postliquefaction consequences. The simplified methods for liquefaction triggering and consequence assessment that are typically employed in practice today are limited in their predictive capabilities.
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From page 199... ...
Understanding the mechanisms of post-liquefaction soil behavior is fundamental to understanding the dependency of post-liquefaction residual strength on consolidation stress; this includes the potential for a threshold value of soil resistance (e.g., normalized SPT blow count or CPT tip resistance) above
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From page 200... ...
Society has benefited from widespread acceptance and application of these approaches, but now those approaches to liquefaction assessment are changing in response to new data, new analytical methods, and recent developments in earthquake engineering. The preceding recommendations stress the importance of implementing existing methods in accordance with their stated procedures, using high-quality data that depict spatial variations at a site, and making that high-quality data available publicly after careful review and vetting.
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