Environmental Engineering Reference
In-Depth Information
Figure 12.26.
Shear wave clean sand base cyclic resistance ratio curve for magnitude 7.5 earthquake
with data from compiled case histories (Youd et al., 2001, from Andrus and Stokoe,
2000, reproduced with permission of ASCE).
12.4.3.7 Earthquake magnitude scaling factors and factor of safety against
liquefaction
The procedures outlined in Sections 12.4.3.4 to 12.4.3.6 give CRR 7.5 , Cyclic Resistance
Ratios for M7.5 earthquakes.
Smaller magnitude earthquakes giving the same peak horizontal acceleration are less
likely to initiate liquefaction, because the earthquake will have fewer cycles of motion.
Larger magnitude earthquakes are more likely to initiate liquefaction. This is allowed for
by using a magnitude scaling factor (MSF) in the equation for factor of safety (FS) against
liquefaction:
FS
(CRR
/CSR)MSF
(12.24)
7.5
where CSR
calculated cyclic stress ratio generated by the earthquake shaking; and
CRR 7.5
Cyclic Resistance Ratio for magnitude 7.5 earthquakes.
Youd et al. (2001) present a discussion on MSF and conclude that the original Seed and
Idriss (1982) factors are too conservative for M
7.5. They recommend MSF in the
range shown in Figure 12.27 for M
7.5.
Liu et al. (2001) publish some additional information relating to MSF. Their studies
show MSF lower than the NCEER workshop values for M
7.5. Given this, it would
seem prudent to use the lower bound of the NCEER workshop values in Figure 12.27,
and, for critical studies, consider lower values after reviewing Liu et al. (2001) and the
most recent literature.
 
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