State of the Art and Practice in the Assessment of Earthquake-Induced Soil Liquefaction and Its Consequences (2021) / Chapter Skim
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3 Case Histories
3 Case Histories
Pages 49-74
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From page 49... ...
• Standardized protocols are needed for documenting and interpreting case histories of liquefaction, lateral spreading and flow sliding, and related phenomena. • Appropriate measures of the quality of case history data are needed in case history databases.
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From page 50... ...
The chapter focuses largely on case histories in which an earthquake triggers, or fails to trigger, liquefaction. But the chapter also considers case histories of two of the main consequences of liquefaction: lateral spreading, and the shear strength of a soil that undergoes large deformation subsequent to liquefaction triggering.
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From page 51... ...
; and the series of earthquakes in or near Christchurch, New Zealand, in 2010 and 2011. Other in situ test methods used to characterize soil behavior and stratigraphy for liquefaction case histories include the piezocone penetration test (CPTu)
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From page 52... ...
Of the few case histories of lateral spreading or flow sliding characterized by the CPT, many of the data points are from older and less reliable CPT probes. In the residual shear strength of liquefied soil case history database compiled by Robertson (2010)
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From page 53... ...
. In a simplified procedure, CRR is correlated to one of the in situ test parameters described above (e.g., SPT blow count, CPT tip resistance, or Vs)
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From page 54... ...
. Water ejected from liquefied soils, with or without solid material from those soils, can create or follow underground pathways that are marked by intrusions whether or not the water produces sand boils at the ground surface (Lowe, 1975; Hurst et al., 2011)
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From page 55... ...
at the ground surface; the depth of the groundwater table; the depth of the soil inferred to have liquefied (i.e., the "critical layer") ; a representative SPT blow count (or N-value)
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From page 56... ...
TABLE 3.2 Summary of Recently Compiled Liquefaction Triggering Case History Databases for Level-Ground Conditions Showing Ranges in Values of the Parameters SPT CPT Vs Parameter Cea04a BI14b Mea06c BI14 Kea13d "yes" cases 287 109 133 139 180 "no" cases 124 88 118 44 71 "yes/no" cases 4 3 3 0 2 Critical depth (m) 1.1-20.5 1.8-14.3 1.4-14.0 1.4-11.8 1.1-18.5 Effective overburden stress σ'vo (kPa)
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From page 57... ...
(c) FIGURE 3.1 Plots of normalized in situ test values for case histories as a function of depth for the most recently compiled databases: (a)
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From page 58... ...
Furthermore, interpretation of published field data is complicated by the general failure of the investigators to report Atterberg limits for fine-grained soils that were subject to strong shaking but did not liquefy. Additional field case history data on the performance of fine-grained soils subject to strong shaking, including Atterberg limits on soils that did not liquefy, supplemented by sampling and laboratory testing of the fine- grained soils reported to have liquefied and not liquefied, are needed to develop comprehensive criteria regarding the liquefaction susceptibility of fine-grained soils and the suitability of various procedures for evaluating liquefaction potential.
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From page 59... ...
Early case history databases sometimes contained multiple critical layers extracted from a single boring or sounding (e.g., Tokimatsu and Yoshimi, 1983; Yegian and Vitelli, 1983; Seed et al., 1984; Stark and Olson, 1995)
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From page 60... ...
Water expelled from a liquefied soil, with or without material from that soil itself, can entrain material from overlying strata as it flows from the critical layer to the ground surface. For example, the 1989 Loma Prieta earthquake produced boils of mud that erupted in an area where liquefiable sand underlies estuarine mud.
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From page 61... ...
In lieu of detailed site response analyses, simplified procedures often are used to estimate the seismic demand imposed on the critical layer. Several potential sources of ground motion intensity data of varying degrees of uncertainty are used to estimate the intensity data for the case histories.
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From page 62... ...
As may be observed from Table 3.2, the plots shown in Figure 3.1, and in Appendix C, the maximum depth to the center of the critical layer listed in recently compiled case history databases is 20.5 meters, but some researchers place the maximum value for that same case history at considerably shallower depth.2 The next deepest cited cases for liquefaction are approximately 18 meters for two sites (Kayen et al., 2013) , but it is uncertain whether these two sites are included in the other databases.
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From page 63... ...
As a result, data are not collected for those nearby profiles that may have liquefied without surface manifestations; that may be susceptible to liquefaction but did not liquefy under the specific earthquake loads; or that are not liquefiable. To minimize bias, the numbers of "yes" and "no" cases need to be balanced when developing liquefaction resistance correlations (e.g., CRR curves)
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From page 64... ...
This predicament adds to the importance of laboratory and analytical studies of the impact on liquefaction behavior of the nature of ground motions in these regions. Influence of Soil Age on Liquefaction Potential The vast majority of case histories in the liquefaction triggering databases represent either man-made fills or Holocene alluvial and fluvial sediments (Robertson and Wride, 1998; Youd et al., 2001)
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From page 65... ...
Most of the sites were equipped with only ground surface instruments, but a few of those locations also include downhole instruments in vertical arrays. Vertical Arrays Vertical ground motion instrument arrays, in which strong motion instruments are placed at the ground surface and at one or more depths in nearby boreholes, can provide excellent opportunities to understand the seismic response of soil profiles and of individual soil layers between pairs of instruments at adjacent depths.4 They also provide data on the ground shaking intensity at the time liquefaction is triggered.
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From page 66... ...
, and the Seattle liquefaction array.a ________ a See http://nees.ucsb.edu/facilities/seattle-liquefaction-array. Sources of bias in lateral spread case history databases are similar to those in liquefaction triggering databases (e.g., tectonic setting, geologic age and setting, pre- versus post-earthquake characterization of soil profiles, interdependence of case histories)
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From page 67... ...
. Lateral spread case history databases have not been subject to the same level of scrutiny as have liquefaction triggering databases.
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From page 68... ...
of granular soils are significantly smaller and contain larger uncertainties than are those for liquefaction triggering and lateral spreading. One of the first, if not the first, field case history databases for residual shear strength consisted of just 12 case histories and included earthquake-induced failures of several dams, dikes, embankments, natural slopes and lateral spreads, an earthquake-induced bearing capacity failure of a four-story apartment building, and the failure of two hydraulic-fill dams under construction (Seed, 1987)
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From page 69... ...
2014. Lateral spread deformations from the 2010-2011 New Zealand earthquakes measured from satellite images and optical image correlation.
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From page 70... ...
, on the other hand, stated that their analyses showed that residual shear strengths back-calculated from lateral spread cases were in good agreement with those from the Olson and Stark (2002) residual shear strength case history database.
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From page 71... ...
TABLE 3.5 Example Checklist for Documenting Liquefaction and Related Phenomena Case Histories Data Type Desired Documentation Comments Site overview Longitude and Latitude of Site Topography, Ground Slope Proximity to topographic irregularities Presence/Proximity of Structures Building structures, buried infrastructure, embankments, etc. Geologic Natural or Man-Made Fill Construction records for fills (dates, setting and site geology methods of placement)
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From page 72... ...
For lateral spreading and residual shear strength case histories, LiDAR scans and high-resolution aerial photographs for both pre- and post-event or topographic surveys. Ground Motions Evidence of rapid changes in frequency content, dilation-induced acceleration spikes Site Characterization Borings Number, locations relative to liquefaction features, drilling data (i.e., rotary wash, hollow stem, casing)
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From page 73... ...
Case histories for triggering, lateral spreading, and settlement will be included. The NGL documentation effort will also include laboratory, physical model, field, and numerical studies on key aspects of liquefaction triggering and related phenomena that are poorly constrained by the current field case history database.
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From page 74... ...
Engineering practice will improve when case history documentation consistently includes factors that describe the quality of the data, and when case history quality ratings are considered during development, calibration, and validation of post-liquefaction residual shear strength models. Development of the quality rating can be left to individual investigators developing correlations, provided their case history documentation includes those factors necessary to develop a rating system.
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