State of the Art and Practice in the Assessment of Earthquake-Induced Soil Liquefaction and Its Consequences (2021) / Chapter Skim
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6 Residual Shear Strength of Liquefied Soil
6 Residual Shear Strength of Liquefied Soil
Pages 126-135
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From page 126... ...
Fundamental differences among approaches used to establish correlations include whether the residual strength is dependent on the pre-earthquake vertical effective stress and whether a correction to the normalized standard penetration test blow count is needed. • Use of several different correlations when evaluating the residual strength is warranted considering the different approaches to characterizing the residual strength and the substantial uncertainty associated with the resulting correlations.
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From page 127... ...
RESIDUAL SHEAR STRENGTH OF SANDY SOILS Several researchers have conducted field and laboratory studies to establish relations between the residual strength and parameters such as SPT or CPT resistance, effective stress prior to the earthquake, and fines content. Table 6.1 summarizes the studies on which residual shear strength relationships most commonly used in practice today are based.
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From page 128... ...
Seed (1987) proposed a correlation between residual shear strength and SPT resistance that related the shear strength back-calculated from 12 case histories of flow sliding to what he termed the equivalent clean-sand normalized SPT blow count, (N1)
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From page 129... ...
They concluded that the residual strength ratio was independent of fines content and recommended that no adjustment be applied to the SPT blow count for fines content. The residual shear strengths back-calculated by Olson and Stark (2002)
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From page 130... ...
Idriss and Boulanger (2007) also provide a relationship between residual strength ratio and equivalent clean-sand normalized CPT tip resistance, qc1Ncs, drawn to be consistent with their (N1)
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From page 131... ...
The previously described procedures (see, e.g., Olson and Stark, 2002; Idriss and Boulanger, 2007; Robertson, 2010) assumed the ratio of the residual strength to the pre-earthquake vertical effective stress linearly related to a resistance parameter (e.g., SPT blow count or CPT penetration resistance)
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From page 132... ...
This material may be found at http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000286. FIGURE 6.5 Variation in median of post-liquefaction strength with normalized SPT blow count and initial vertical effective stress by Kramer (2008)
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From page 133... ...
The few available data for gravelly soils appear to be consistent with the assumption that the resistance to liquefaction triggering and the residual strength of gravelly soils are similar to those of sandy soils of the same equivalent penetration resistance2 (see, e.g., Harder, 1988; Andrus and Youd, 1989)
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From page 134... ...
In addition, the many factors that control the residual strength of liquefied soil masses in the field suggest that there will always be large scatter in any correlation between residual shear strength and a simple measure of penetration resistance or a combination of penetration resistance and initial effective stress. The committee notes that Figure 6.1 by Seed and Harder (1990)
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From page 135... ...
In the future, it may be possible to address the issue of residual shear strength as a system response through the use of the computational mechanics tools discussed in Chapter 8 of this report, combined with accurate modeling of the key features that determine the response of a system involving soil liquefaction. This capability, however, is well beyond the present state of the practice.
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